A pathologist (K.S.) reviewed histologic slides for peritoneal involvement by tumor cells for 118 patients with stage II colon cancer. Patients were followed up for a median of 6 years. Tumor cells were found free in the peritoneal space in 16 cases (13.6%). The presence of cancer cells free in the peritoneal space was associated with lymphovascular invasion (P = .001) and neural invasion (P < .001). The overall 5-year survival was 80% in the patient population, but was 39% and 86% for those with and without tumor cells free in the peritoneal space, respectively (P < .0001). Multivariate analysis confirmed that free tumor cells within the peritoneal space (P < .0001) and lymphovascular invasion (P = .007) were related independently to outcome. Peritoneal involvement with tumor cells free in the peritoneal space in stage II colon cancer is a powerful indicator of outcome; patients have a survival similar to that for patients with stage III disease.