The Peritoneal Surface Oncology Group International (PSOGI) recommends pathologic reporting of tumor cellularity in patients with pseudomyxoma peritonei (PMP) undergoing cytoreductive surgery and hyperthermic intraperitoneal chemoperfusion (CRS-HIPEC). We investigated the prognostic significance of PMP cellularity, or lack thereof (acellular mucin), following CRS-HIPEC.