Improved survival has been reported for diffuse malignant peritoneal mesothelioma (DMPM) treated by cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC). The issue of treatment failure has never been extensively addressed. The present study assessed the failure pattern, management, and outcome of progressive DMPM following comprehensive treatment. Clinical data on 70 patients with DMPM undergoing cytoreduction and HIPEC were prospectively collected; after a median follow-up of 43 months, disease progression occurred in 38 patients. Progressive disease distribution in 13 abdominopelvic regions was analyzed. In 28 patients undergoing adequate cytoreduction (residual tumor < or =2.5 mm), clinicopathological factors correlating to disease progression in each region were investigated. Median time to progression was 9 months [95% confidence interval (CI) 1.6-35.9]. Median survival from progression was 8 months (95% CI 4-16.2). The failure pattern was categorized as peritoneal progression (n = 31), liver metastases (n = 1), abdominal lymph-node involvement (n = 2), pleural seeding (n = 4). Small bowel was the single site most commonly involved (n = 27). Residual tumor < or =2.5 mm (versus no visible) was the only independent risk factor for disease progression in epigastric region (P = 0.047), upper ileum (P = 0.029), upper jejunum (P = 0.034), and lower jejunum (P = 0.002). Progressive disease was treated with second HIPEC in 3 patients, debulking in 4, systemic chemotherapy in 16, and supportive care in 15. At multivariate analysis, time to progression <9 months (P = 0.009), poor performance status (P = 0.005), and supportive care (P = 0.003) correlated to reduced survival from progression. We conclude that minimal residual disease, compared with macroscopically complete cytoreduction, correlated to failure in critical anatomical areas, suggesting the need for maximal cytoreductive surgical efforts. In selected patients, aggressive management of progressive disease seems worthwhile.