OBJECTIVES:  Treatment outcomes have improved greatly over the last decade for patients with metastatic colorectal cancer (mCRC) due to the advances in systemic chemotherapies, targeted agents, and supportive care. We aimed to describe contemporary real-world first line (1L) treatment among patients with mCRC. METHODS:  Patients with mCRC diagnosed from 2012–2014 (ICD-9 codes 153.x, 154.0x, or 154.1x and 197.x–198.x) were identified from a US healthcare claims database consisting of 129 million unique covered patient lives. Patients were classified into treatment groups based on the 1L treatment received. The end of 1L was defined as addition of new drug(s) to the original treatment outside of the first 30 days of treatment; if an additional agent was added to a fluoropyrimidine (FP) backbone within 60 days, then the regimen was classified as a combination instead of incrementing the line of therapy. Time from diagnosis to initiation of 1L was calculated for each treatment group. RESULTS:  There were 4,527 mCRC patients identified (mean age at diagnosis, 61.2 years; 54% male) who initiated 1L therapy. On average (mean, SD), patients were followed for 12.8 months (8.47 months) after diagnosis. The most common 1L regimen (39%) consisted of FP + chemotherapy, followed by biologic + FP + chemotherapy (36%), FP monotherapy (21%), and biologic + FP (5%). Across treatment groups, half of patients initiated 1L within 39 days of diagnosis (range of medians across treatment groups: 15 days to 43 days; all pairwise comparisons, p<0.05). CONCLUSIONS:  These real world data show substantial variability in treatments received in 1L and time to 1L initiation among patients with mCRC. Despite published guidelines, just over 1/3 of patients received a chemotherapy doublet plus biologic. Further research is needed to understand the surprisingly low penetration of biologics into 1L.