Background Before 2016, patients with isolated synchronous colorectal peritoneal metastases (PMCRC) diagnosed in expert centers had a higher odds of undergoing cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (CRS-HIPEC) and better overall survival (OS) than those diagnosed in referring centers. Nationwide efforts were initiated to increase awareness and improve referral networks. Methods This nationwide study aimed to evaluate whether the between-center differences in odds of undergoing CRS-HIPEC and OS have reduced since these national efforts were initiated. All patients with isolated synchronous PMCRC diagnosed between 2009 and 2021 were identified from the Netherlands Cancer Registry. Associations between hospital of diagnosis and the odds of undergoing CRS-HIPEC, as well as OS, were assessed using multilevel multivariable regression analyses for two periods (2009–2015 and 2016–2021). Results In total, 3948 patients were included. The percentage of patients undergoing CRS-HIPEC increased from 17.2% in 2009–2015 (25.4% in expert centers, 16.5% in referring centers), to 23.4% in 2016–2021 (30.2% in expert centers, 22.6% in referring centers). In 2009–2015, compared with diagnosis in a referring center, diagnosis in a HIPEC center showed a higher odds of undergoing CRS-HIPEC (odds ratio OR 1.64, 95% confidence interval CI 1.02–2.67) and better survival (hazard ratio HR 0.80, 95% CI 0.66–0.96). In 2016–2021, there were no differences in the odds of undergoing CRS-HIPEC between patients diagnosed in HIPEC centers versus referring centers (OR 1.27, 95% CI 0.76–2.13) and survival (HR 1.00, 95% CI 0.76–1.32). Conclusion Previously observed differences in odds of undergoing CRS-HIPEC were no longer present. Increased awareness and the harmonization of treatment for PMCRC may have contributed to equal access to care and a similar chance of survival at a national level.