Abstract Background Selected patients with colorectal peritoneal metastases are treated with cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). The concentration of intraperitoneal chemotherapy reflects the administered dose and perfusate volume. The aim of this study was to calculate intraperitoneal chemotherapy concentration during HIPEC and see whether this was related to clinical outcomes. Methods An observational multicentre study included consecutive patients with colorectal peritoneal metastases who were treated with CRS–HIPEC between 2010 and 2018 at three Dutch centres. Data were retrieved from prospectively developed databases. Chemotherapy dose and total circulating volumes of carrier solution were used to calculate chemotherapy concentrations. Postoperative complications, disease-free and overall survival were correlated with intraoperative chemotherapy concentrations. Univariable and multivariable logistic regression, Cox regression and survival analyses were performed. Results Of 320 patients, 220 received intraperitoneal mitomycin C (MMC) and 100 received oxaliplatin. Median perfusate volume for HIPEC was 5·0 (range 0·7–10·0) litres. Median intraperitoneal chemotherapy concentration was 13·3 (range 7·0–76·0) mg/l for MMC and 156·0 (91·9–377·6) mg/l in patients treated with oxaliplatin. Grade III or higher complications occurred in 75 patients (23·4 per cent). Median overall survival was 36·9 (i.q.r. 19·5–62·9) months. Intraperitoneal chemotherapy concentrations were not associated with postoperative complications or survival. Conclusion CRS–HIPEC was performed with a wide variation in intraperitoneal chemotherapy concentrations that were not associated with complications or survival.