The clinical and pathologic features of 16 malignant Brenner tumors (MBT) having an associated benign Brenner component were compared with 29 primary ovarian transitional cell carcinomas (TCC), neoplasms differing from MBT only in that a benign Brenner component was absent. Transitional cell carcinoma represented a more aggressive neoplasm. Twenty of twenty-nine (69%) presented in advanced stages (II-IV) compared with only three of sixteen (19%) MBT. Among stage IA tumors, only three of seven (43%) patients with TCC were well at last contact, compared with nine of eleven (88%) patients with Stage IA MBT. In addition to not having a benign Brenner component, TCC lacked the prominent stromal calcification common in most benign and malignant Brenner tumors. Transitional cell carcinoma is sufficiently different from MBT in that it is reasonable to suppose that ovarian TCC arises directly from pluripotential surface epithelium of the ovary and from cells with urothelial potential, rather than from a benign or proliferative Brenner tumor precursor.