Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS + HIPEC) can result in long-term survival for selected patients with colorectal peritoneal metastases (PM). Most patients are additionally treated with systemic chemotherapy, but timing (adjuvant vs. preoperative) varies between treatment centers. This study aimed to compare short- and long-term outcomes for patients with synchronous colorectal PM undergoing CRS + HIPEC who received preoperative or adjuvant chemotherapy.This study enrolled patients with synchronous colorectal PM who underwent macroscopically complete or near complete CRS + HIPEC. Data were collected from a prospective database containing all patients between 2007 and 2014. Perioperative outcome and survival were compared between patients who underwent adjuvant chemotherapy (adjuvant strategy [AS]) and those who had preoperative chemotherapy followed by adjuvant systemic chemotherapy if possible (preoperative strategy [PS]).The study enrolled 91 patients, 25 (28 %) of whom received preoperative chemotherapy. The peritoneal cancer index (PCI) score was lower and the operation length shorter for the patients receiving preoperative chemotherapy (both p = 0.02). The complication rates were comparable between the two groups. The median survival after diagnosis was 38.6 months in the AS group, whereas median survival was not reached in the PS group (p < 0.01). The 3-year overall survival rates were 50 and 89 %, respectively. After correction for other significant prognostic factors, preoperative chemotherapy was independently associated with improved survival (HR 0.23; 95 % confidence interval, 0.07-0.75; p = 0.01).Treatment with preoperative chemotherapy was associated with improved long-term survival after CRS + HIPEC compared with adjuvant chemotherapy. Ideally, a randomized controlled trial should be performed to investigate the optimal timing of systemic chemotherapy for colorectal PM patients.