Most lymphomas arising in the ovary are diffuse large B-cell or Burkitt lymphomas. Follicular lymphomas of the ovary are rare, and their clinicopathologic features are incompletely understood. We investigated clinical, morphologic, immuno-phenotypic, and genetic features of follicular lymphomas initially diagnosed in the ovary in 16 women. We performed immunohistochemistry for CD20, CD3, CD10, BCL6, IRF4/MUM1, and BCL2 and interphase fluorescence in situ hybridization for translocations involving BCL2, BCL6, and IRF4. Clustering was performed on the basis of clinicopathologic and genetic variables using Cluster 3.0. Ages ranged from 42 to 73 years. Unsupervised hierarchical clustering analysis revealed 2 distinct groups of patients. One group (group A) included 7 cases, which were negative or weakly positive for BCL2 protein and lacked IGH@/BCL2 translocations (6 cases evaluable). Four patients were of grade 3A, and 3 patients were of grade 2. Four had stage IE disease with unilateral ovarian involvement (subgroup A(1)), and the stage was unknown in 3 patients (subgroup A(2)). The second group (group B) included 9 cases of low histologic grade, which strongly expressed BCL2 protein and had IGH@/BCL2 translocations (7 cases evaluable). Six patients had stage III/IV disease, 2 had stage II disease, and the stage was unknown in 1 patient. Although follow-up intervals were limited, patients with higher-grade/ low-stage disease tended to have favorable outcomes. These data indicate 2 distinct types of follicular lymphomas presenting in the ovary: a low-grade/high-stage/BCL2-positive group and a higher-grade/low-stage/BCL2-negative group. This latter group likely has distinct biological and immunologic characteristics, as has been suggested for higher-grade/ low-stage follicular lymphomas presenting at other extranodal sites.