OBJECTIVE There have been few studies concerning the clinical pathology of squamous cell carcinoma arising from ovarian mature cystic teratoma. Thus, the objective of this study is to determine clinicopathologic factors affecting survival in this rare tumor. METHODS From September 1979 to June 1996, 37 patients with squamous cell carcinoma arising from ovarian mature cystic teratoma were treated by the Tokai Ovarian Tumor Study Group. A retrospective clinicopathologic and survival analysis of these patients was performed. The mode of infiltration was classified into expansive, moderately diffused, and diffused patterns. RESULTS Although the 5-year survival rate was 94.7% and 80.0% for stage I and II patients, respectively, 12 of 13 patients with stage III died within 20 months (P = .0001). A significant difference was also observed between the survival of the groups with and without residual tumor at surgery (P = .0001). Pathologic features, grade, mode of infiltration, and vascular involvement were significant factors by univariate analysis. Multivariate analysis showed significant differences in survival related to grade (P = .0154) and mode of infiltration (P = .0053). The preoperative squamous cell carcinoma antigen level was significantly higher in the patients with squamous cell carcinoma arising from mature cystic teratoma than in patients with mature cystic teratoma (P < .0001). CONCLUSIONS This study suggests that pathologic factors, grade, and mode of infiltration can provide valuable information for predicting the survival of patients with squamous cell carcinoma arising from mature cystic teratoma. In addition, squamous cell carcinoma antigen may be a useful marker to detect this disease preoperatively.