OBJECTIVES: Explore factors associated with conversion from laparoscopic to open approach in left-sided colon resections and analyze differences in hospital cost, length of stay(LOS), and operating room time(ORT) for Lap-Conversion, Open-Planned and Lap-Successful approaches.  METHODS: The Premier Perspective^® Database containing billing data from ~600 hospitals in the U.S. was analyzed. All patients undergoing left-hemicolectomy or sigmoidectomy from 2009-2014 were identified. Lap-Conversion was identified by ICD9-code(V64.41) or when a laparoscopic and open procedure code occurred simultaneously. Lap-Conversion incidence was calculated for all procedures with evidence of a laparoscopic approach (Lap-Attempted). Resource utilization parameters of ORT, LOS, and hospital cost (2014 US-Dollars) were analyzed. For Lap-Attempted procedures, patient, provider, and procedure factors associated with conversion were explored in a multivariable model. Similar models were used on all procedures to evaluate the effect of surgical approach on LOS, ORT, and cost.  All statistical analyses accounted for clustering within hospitals; p-values <0.05 were considered significant.      RESULTS: A total of 80,078 patients undergoing left-hemicolectomy(18,279) or sigmoidectomy(61,799) were identified. There were 34,795 Lap-Attempted procedures and the incidence of Lap-Conversion was 16.86%(95%CI[15.90,17.82]). Adjusted mean LOS(SE) for Lap-Conversion was 9.1(0.1) days compared to 6.8(0.1) and 9.2(0.1) for Lap-Successful and Open-Planned, respectively.  Adjusted mean cost(SE) followed a similar trend: $24,317($397) for Lap-Conversion, $20,603($284) and $24,317($323) for Lap-Successful and Open-Planned.  Adjusted mean ORT(SE) for Lap-Conversion was 244(5.2) minutes compared to 218(4.1) and 194(3.3) for Lap-Successful and Open-Planned.  Risk factors associated with Lap-Conversion included: left-hemicolectomy OR=1.44(95%CI[1.30,1.60]), diverticulitis OR=1.16(95%CI[1.052,1.28]) and inflammatory bowel disease (IBD) OR=1.39(95%CI[1.06,1.83]). Robotic-assistance OR=0.42(95%CI[0.33,0.55]) and elective procedures OR=0.54(95%CI[0.49,0.60)] were associated with decreased risk.   CONCLUSIONS: Lap-Conversion resulted in the disappearance of LOS and cost benefits of the laparoscopic approach. Lap-Conversion had longer ORT, but similar LOS and cost compared to Open-Planned approaches. Lap-Conversion and Open-Planned were associated with similar significant increases in LOS and costs compared to Lap-Successful.