diff --git a/lib/editor-decorator.coffee b/lib/editor-decorator.coffee
new file mode 100644
index 0000000..e2d242f
--- /dev/null
+++ b/lib/editor-decorator.coffee
@@ -0,0 +1,20 @@
+# Decorate any lines within an {Editor} that correspond to an active {Stacktrace}.
+
+{Stacktrace} = require './stacktrace'
+
+markers = []
+
+module.exports = (editor) ->
+  m.destroy() for m in markers
+  markers = []
+
+  active = Stacktrace.getActivated()
+  return unless active?
+
+  for frame in active.frames
+    if frame.realPath is editor.getPath()
+      range = editor.getBuffer().rangeForRow frame.bufferLineNumber()
+      marker = editor.markBufferRange range
+      editor.decorateMarker marker, type: 'line', class: 'line-stackframe'
+      editor.decorateMarker marker, type: 'gutter', class: 'gutter-stackframe'
+      markers.push marker
diff --git a/lib/main.coffee b/lib/main.coffee
index cf64fba..f24b80c 100644
--- a/lib/main.coffee
+++ b/lib/main.coffee
@@ -1,6 +1,7 @@
 EnterDialog = require './enter-dialog'
 {Stacktrace} = require './stacktrace'
 {StacktraceView} = require './stacktrace-view'
+editorDecorator = require './editor-decorator'
 
 module.exports =
 
@@ -13,6 +14,10 @@ module.exports =
       text = (s.getText() for s in (selections or [])).join ''
       atom.emit 'stacktrace:accept-trace', trace: text
 
+    atom.workspace.eachEditor editorDecorator
+    Stacktrace.on 'active-changed', ->
+      editorDecorator(e) for e in atom.workspace.getEditors()
+
     StacktraceView.registerIn(atom.workspace)
 
     atom.on 'stacktrace:accept-trace', ({trace}) =>
@@ -21,6 +26,7 @@ module.exports =
         atom.workspace.open trace.getUrl()
 
   deactivate: ->
+    Stacktrace.off 'active-changed'
     atom.off 'stacktrace:accept-trace'
 
   serialize: ->
diff --git a/lib/stacktrace.coffee b/lib/stacktrace.coffee
index 413f38e..14aaf8e 100644
--- a/lib/stacktrace.coffee
+++ b/lib/stacktrace.coffee
@@ -92,6 +92,10 @@ class Frame
   constructor: (@rawLine, @rawPath, @lineNumber, @functionName) ->
     @realPath = @rawPath
 
+  # Public: Return the zero-indexed line number.
+  #
+  bufferLineNumber: -> @lineNumber - 1
+
   # Public: Asynchronously collect n lines of context around the specified line number in this
   # frame's source file.
   #
diff --git a/spec/editor-marker-spec.coffee b/spec/editor-marker-spec.coffee
new file mode 100644
index 0000000..425a769
--- /dev/null
+++ b/spec/editor-marker-spec.coffee
@@ -0,0 +1,64 @@
+path = require 'path'
+{Editor, WorkspaceView} = require 'atom'
+
+{Stacktrace, Frame} = require '../lib/stacktrace'
+editorDecorator = require '../lib/editor-decorator'
+
+framePath = (fname) -> path.join __dirname, 'fixtures', fname
+
+frames = [
+  new Frame('raw0', framePath('bottom.rb'), 12, 'botfunc')
+  new Frame('raw1', framePath('middle.rb'), 42, 'midfunc')
+  new Frame('raw2', framePath('top.rb'), 37, 'topfunc')
+  new Frame('raw3', framePath('middle.rb'), 5, 'otherfunc')
+]
+trace = new Stacktrace(frames, 'Boom')
+
+describe 'editorDecorator', ->
+  [editor, editorView] = []
+
+  beforeEach ->
+    atom.workspaceView = new WorkspaceView
+
+  afterEach ->
+    Stacktrace.getActivated()?.deactivate()
+
+  withEditorOn = (fname, callback) ->
+    waitsForPromise ->
+      atom.workspace.open(framePath fname)
+
+    runs ->
+      atom.workspaceView.attachToDom()
+      editorView = atom.workspaceView.getActiveView()
+      editor = editorView.getEditor()
+      callback()
+
+  it 'does nothing if there is no active trace', ->
+    expect(Stacktrace.getActivated()).toBeNull()
+
+    withEditorOn 'bottom.rb', ->
+      editorDecorator(editor)
+      expect(editorView.find '.line.line-stackframe').toHaveLength 0
+
+  describe 'with an active trace', ->
+
+    beforeEach -> trace.activate()
+
+    it "does nothing if the file doesn't appear in the active trace", ->
+      withEditorOn 'context.txt', ->
+        editorDecorator(editor)
+        expect(editorView.find '.line.line-stackframe').toHaveLength 0
+
+    it 'decorates stackframe lines in applicable editors', ->
+      withEditorOn 'bottom.rb', ->
+        editorDecorator(editor)
+        decorated = editorView.find '.line.line-stackframe'
+        expect(decorated).toHaveLength 1
+        expect(decorated.text()).toEqual("  puts 'this is the stack line'")
+
+    it 'removes prior decorations when deactivated', ->
+      withEditorOn 'bottom.rb', ->
+        editorDecorator(editor)
+        trace.deactivate()
+        editorDecorator(editor)
+        expect(editorView.find '.line.line-stackframe').toHaveLength 0
diff --git a/spec/fixtures/bottom.rb b/spec/fixtures/bottom.rb
new file mode 100644
index 0000000..fb32573
--- /dev/null
+++ b/spec/fixtures/bottom.rb
@@ -0,0 +1,14 @@
+# This isn't a real Ruby file. It's a test fixture I can reference in other places.
+
+
+
+
+
+
+
+
+def botfunc
+  before = true
+  puts 'this is the stack line'
+  after = false
+end
diff --git a/spec/fixtures/middle.rb b/spec/fixtures/middle.rb
new file mode 100644
index 0000000..d8d7ee3
--- /dev/null
+++ b/spec/fixtures/middle.rb
@@ -0,0 +1,43 @@
+# This isn't a real Ruby file. It's a test fixture I can reference in other places.
+# This one has two lines in the "stack trace".
+
+def otherfunc
+  puts 'this is the line'
+  # and more stuff
+end
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+def botfunc
+  # more things
+  puts 'this is the line'
+end
diff --git a/spec/fixtures/top.rb b/spec/fixtures/top.rb
new file mode 100644
index 0000000..d0c6839
--- /dev/null
+++ b/spec/fixtures/top.rb
@@ -0,0 +1,38 @@
+# This isn't a real Ruby file. It's a test fixture I can reference in other places.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+def topfunc
+  # things
+  puts 'this is the line'
+end
diff --git a/stylesheets/stacktrace.less b/stylesheets/stacktrace.less
index 282fe3c..5bfc3c8 100644
--- a/stylesheets/stacktrace.less
+++ b/stylesheets/stacktrace.less
@@ -3,6 +3,10 @@
 // See https://github.com/atom/atom-dark-ui/blob/master/stylesheets/ui-variables.less
 // for a full listing of what's available.
 @import "ui-variables";
+@import "syntax-variables";
+
+@stackframe-background: mix(@background-color-info, @syntax-background-color, 40%);
+@stackframe-gutter-background: mix(@background-color-info, @syntax-gutter-background-color, 40%);
 
 .stacktrace {
   &.enter-dialog .editor {
@@ -45,3 +49,13 @@
   }
 
 }
+
+.editor {
+  .line.line-stackframe {
+    background: @stackframe-background;
+  }
+
+  .gutter .gutter-stackframe {
+    background: @stackframe-gutter-background;
+  }
+}