INTRODUCTION: The optimal timing of primary and metastatic tumor management in patients with synchronous hepatic colorectal metastases remains controversial. We aimed to compare perioperative outcomes of simultaneous colorectal/liver resection (SCLR) with isolated resections utilizing a national clinical database. METHODS: NSQIP data from 2005 to 2009 were examined to construct risk-adjusted generalized linear models and to calculate group-specific predicted estimates. These were used to compare 30-day perioperative outcomes among patients undergoing SCLR with colorectal (CR) and liver resections (LR) only in patients with metastatic colorectal cancer. RESULTS: A total of 3,983 patients were identified, who underwent SCLR (192), LR (1,857), or CR (1,934). Rectal resection was performed in 45 (23.4 %) SCLR patients and 269 (13.9 %) CR patients (p < 0.001). Major hepatectomy was performed in 69 (35.9 %) SCLR patients and 774 (41.7 %) LR patients (p = 0.12). Median adjusted operation time (SCLR: 273 min, 95 % CI: 253-295; CR: 172, CI: 168-177; LR: 222, CI: 217-228; p < 0.001) and median adjusted length of hospital stay (SCLR: 9.5 days, CI: 8.8-10.4; CR: 8.1, CI: 7.9-8.3; LR: 6.4, CI: 6.3-6.6; p < 0.001) were longer for SCLR compared to CR and LR. Adjusted predicted risks for at least one postoperative complication were higher in SCLR (36.3 %) than in CR (26.6 %) and LR (19.8 %) (p < 0.003), mostly due to infectious/cardiopulmonary issues. DISCUSSION: In SCLR patients, the risk of 30-day adverse outcomes is higher, and median operation time as well as length of hospital stay is longer compared to CR and LR patients. However, the expected combined morbidities of staged procedures though likely favor SCLR in carefully selected patients undergoing even complex hepatic and colorectal resections and should be considered.