diff --git a/bulk_insert.py b/bulk_insert.py
index 6c8bd67..8a8eab9 100644
--- a/bulk_insert.py
+++ b/bulk_insert.py
@@ -26,7 +26,7 @@ class Type:
 
 # User-configurable thresholds for when to send queries to Redis
 class Configs(object):
-    def __init__(self, max_token_count, max_buffer_size, max_token_size):
+    def __init__(self, max_token_count, max_buffer_size, max_token_size, skip_invalid_nodes):
         # Maximum number of tokens per query
         # 1024 * 1024 is the hard-coded Redis maximum. We'll set a slightly lower limit so
         # that we can safely ignore tokens that aren't binary strings
@@ -38,6 +38,8 @@ def __init__(self, max_token_count, max_buffer_size, max_token_size):
         # 512 megabytes is a hard-coded Redis maximum
         self.max_token_size = min(max_token_size * 1000000, 512 * 1000000)
 
+        self.skip_invalid_nodes = skip_invalid_nodes
+
 # QueryBuffer is the class that processes input CSVs and emits their binary formats to the Redis client.
 class QueryBuffer(object):
     def __init__(self, graphname, client):
@@ -192,9 +194,10 @@ def process_entities(self, expected_col_count):
                 # Add identifier->ID pair to dictionary if we are building relations
                 if NODE_DICT is not None:
                     if row[0] in NODE_DICT:
-                        print("Node identifier '%s' was used multiple times - second occurrence at %s:%d"
+                        sys.stderr.write("Node identifier '%s' was used multiple times - second occurrence at %s:%d\n"
                             % (row[0], self.infile.name, self.reader.line_num))
-                        exit(1)
+                        if CONFIGS.skip_invalid_nodes is False:
+                            exit(1)
                     NODE_DICT[row[0]] = TOP_NODE_ID
                     TOP_NODE_ID += 1
                 row_binary = self.pack_props(row)
@@ -329,8 +332,9 @@ def process_entity_csvs(cls, csvs):
 @click.option('--max-buffer-size', '-b', default=2048, help='max buffer size in megabytes (default 2048)')
 @click.option('--max-token-size', '-t', default=500, help='max size of each token in megabytes (default 500, max 512)')
 @click.option('--quote-minimal/--no-quote-minimal', '-q/-d', default=False, help='only quote those fields which contain special characters such as delimiter, quotechar or any of the characters in lineterminator')
+@click.option('--skip-invalid-nodes', '-s', default=False, is_flag=True, help='ignore nodes that use previously defined IDs')
 
-def bulk_insert(graph, host, port, password, nodes, relations, max_token_count, max_buffer_size, max_token_size, quote_minimal):
+def bulk_insert(graph, host, port, password, nodes, relations, max_token_count, max_buffer_size, max_token_size, quote_minimal, skip_invalid_nodes):
     global CONFIGS
     global NODE_DICT
     global TOP_NODE_ID
@@ -346,7 +350,7 @@ def bulk_insert(graph, host, port, password, nodes, relations, max_token_count,
         QUOTING=csv.QUOTE_NONE 
 
     TOP_NODE_ID = 0 # reset global ID variable (in case we are calling bulk_insert from unit tests)
-    CONFIGS = Configs(max_token_count, max_buffer_size, max_token_size)
+    CONFIGS = Configs(max_token_count, max_buffer_size, max_token_size, skip_invalid_nodes)
 
     start_time = timer()
     # Attempt to connect to Redis server