diff --git a/ENVTEMPLATE.sh b/ENVTEMPLATE.sh
index 48cdf4a..1278be2 100644
--- a/ENVTEMPLATE.sh
+++ b/ENVTEMPLATE.sh
@@ -5,6 +5,7 @@ export CELERY_BROKER='amqp://localhost'
 export WEBHDFS_USER=username
 export WEBHDFS_URL=http://example.com:5000
 export IGV_HTTPFS_URL=http://example.com:9876
+export ALLOW_VCF_OVERWRITES=False
 
 # True for automatic reloading & debugging JS insertion.
 export USE_RELOADER=False
diff --git a/config.py b/config.py
index 2988712..df73df4 100644
--- a/config.py
+++ b/config.py
@@ -1,17 +1,20 @@
 import os
 
-# ensure that false in config isn't interpreted as True
-use_reloader = os.environ.get('USE_RELOADER', False)
-if use_reloader and use_reloader.lower() == 'false':
-    use_reloader = False
-USE_RELOADER = use_reloader
+def handle_false(value):
+    if value and value.lower() == 'false':
+        value = False
+    return value
 
+# ensure that false in config isn't interpreted as True
+USE_RELOADER = handle_false(os.environ.get('USE_RELOADER', False))
 SQLALCHEMY_DATABASE_URI = os.environ['DATABASE_URI']
 PORT = int(os.environ.get('PORT', 5000))
 WEBHDFS_USER = os.environ['WEBHDFS_USER']
 WEBHDFS_URL = os.environ['WEBHDFS_URL']
 IGV_HTTPFS_URL = os.environ['IGV_HTTPFS_URL']
 ALLOW_LOCAL_VCFS = os.environ.get('ALLOW_LOCAL_VCFS', USE_RELOADER)
+ALLOW_VCF_OVERWRITES = handle_false(
+    os.environ.get('ALLOW_VCF_OVERWRITES', False))
 
 TYPEKIT_URL = os.environ.get('TYPEKIT_URL', None)
 
diff --git a/schema.sql b/schema.sql
index 3bee9a2..0145027 100644
--- a/schema.sql
+++ b/schema.sql
@@ -17,7 +17,7 @@ CREATE TABLE vcfs (
 );
 
 CREATE TABLE vcf_annotations (
-       vcf_id BIGINT REFERENCES vcfs NOT NULL,
+       vcf_id BIGINT REFERENCES vcfs ON DELETE CASCADE NOT NULL,
        annotation TEXT NOT NULL,
        type TEXT NOT NULL,
        "contig" TEXT,
@@ -35,7 +35,7 @@ CREATE TABLE data_annotations (
 );
 
 CREATE TABLE genotypes (
-       vcf_id BIGINT REFERENCES vcfs NOT NULL,
+       vcf_id BIGINT REFERENCES vcfs ON DELETE CASCADE NOT NULL,
        sample_name TEXT,
        contig TEXT,
        position INTEGER,
diff --git a/workers/genotype_extractor.py b/workers/genotype_extractor.py
index d642f8b..9240f3b 100644
--- a/workers/genotype_extractor.py
+++ b/workers/genotype_extractor.py
@@ -6,6 +6,7 @@
 adding them to the genotypes table. Finally, determines which columns in the vcf
 actually contain values, and stores a list of them in the vcf table.
 """
+import config
 import json
 from sqlalchemy import create_engine, MetaData
 
@@ -23,8 +24,13 @@ def extractor(run):
     engine, connection, metadata = initialize_database(DATABASE_URI)
 
     if vcf_exists(connection, run):
-        print 'VCF already exists with URI {}'.format(run['vcf_path'])
-        return False
+        if config.ALLOW_VCF_OVERWRITES:
+            was_deleted = delete_vcf(metadata, connection, run['vcf_path'])
+            assert was_deleted, ("Rows should have been deleted if we are "
+                "deleting a VCF that exists")
+        else:
+            print 'VCF already exists with URI {}'.format(run['vcf_path'])
+            return False
 
     reader, header = load_vcf_from_hdfs(run['vcf_path'])
     insert_vcf_metadata(metadata, run, header)
@@ -85,6 +91,12 @@ def get_vcf_id(con, run):
     return con.execute(query).first().id
 
 
+def delete_vcf(metadata, connection, uri):
+    """Delete VCFs with this URI, and return True if rows were deleted."""
+    vcfs = metadata.tables.get('vcfs')
+    result = vcfs.delete().where(vcfs.c.uri == uri).execute()
+    return result.rowcount > 0
+
 def vcf_exists(connection, run):
     """Return True if the VCF exists in the vcfs table, else return False."""
     query = "SELECT * FROM vcfs WHERE uri = '" + run['vcf_path'] + "'"