460 Background: Malignant peritoneal mesothelioma (MPeM) is an aggressive tumor strongly associated with asbestos exposure. We analyzed a large nationwide database to better understand the differences in the demographic and clinical patterns of MPeM and pleural mesothelioma (MPlM). Methods: The National Cancer Database (NCDB) 2010-15 was queried to identify all patients diagnosed with MpeM and MPlM. The demographic and clinical characteristics were compared using Pearson’s chi-square test. Kaplan-Meier method and associated log-rank test were used to compare the unadjusted overall survival of the two malignant mesothelioma (MM) sites. A multivariate Cox regression analysis was done to determine survival difference between the 2 groups. Results: Of the 8,668 patients included in the study, 1,081 (12.5%) had MPeM and 7,587 (87.5%) had MPlM. The MPeM cohort was younger (median age at diagnosis 61 vs 73 years), predominantly females (45.7% vs 23.5%), had a lower Charlson Deyo Comorbidity Score ( > = 1: 24.5% vs 32.1%), had higher percentage of uninsured patients (4% vs 2.2%), was less likely to be treated at a community or comprehensive community center (36.1% vs 47.3%) and had lower proportion of sarcomatous or biphasic histology (9.3% vs 22.4%) compared to MPlM cohort. The MPeM cohort was more likely to receive surgery (56.5% vs 28%) and chemotherapy (68.4% vs 54.5%) but less likely to receive radiation (0.8% vs 11%). The p-value was < 0.001 for all comparisons. The median OS was 19.7 and 9.7 months for patients with MPeM and MPlM, respectively (log-rank p value < 0.001). On multivariate Cox proportional hazards analysis, OS was significantly worse for MPlP compared to MPeP [HR adj: 1.19, 95% confidence interval (CI): 1.09-1.30 (p < 0.001)]. Conclusions: There is paucity of data about clinical characteristics and outcomes of MPeM. Much of our current knowledge about MPeM is extrapolated from MPlM. Our study suggests significant differences in prognostic factors and survival outcomes between the two sites.