Ovarian malignant Brenner tumors are rare neoplasms that are typically admixed with benign and borderline Brenner tumor elements. We report 3 cases of an unusual variant of malignant Brenner tumor where the infiltrative malignant component arose directly from a benign Brenner tumor rather than from borderline elements and did not exhibit a desmoplastic stromal response. Borderline elements were present in 1 case, but the invasive component did not arise from these. Our cases highlight that an absence of a borderline element should not dissuade the pathologist from diagnosing a malignant Brenner tumor.