The diagnosis and subclassification of Sertoli cell tumors (SCT) of the testis are often challenging to general surgical pathologists because of the rarity of the tumors. Immunohistochemical study to date has limited diagnostic value. Nuclear localization of β-catenin, which correlated closely with CTNNB1 gene mutation, was recently reported in SCTs. We investigated the utility of β-catenin nuclear localization in diagnosing SCTs and differentiating them from other testicular sex cord-stromal tumors. Immunohistochemical staining for β-catenin was evaluated in 87 cases of testicular sex cord-stromal tumor: 33 SCTs, not otherwise specified (SCT-NOS) (15 with benign and 18 with malignant features), 10 sclerosing SCTs (SSCT), 5 large cell calcifying SCTs (LCCSCT), 6 Sertoli-stromal cell tumors, 10 Leydig cell tumors, 7 juvenile granulosa cell tumors, 4 adult granulosa cell tumors, and 12 sex cord-stromal tumors, unclassified. Twenty-one of 33 (64%) SCT-NOS, 6 of 10 (60%) SSCTs, and 4 of 6 (67%) Sertoli-stromal cell tumors showed strong, diffuse β-catenin nuclear staining. Nuclear β-catenin positivity was more frequent in SCTs-NOS with benign features than in those with malignant features (93% and 39%, respectively, P=0.13) and, in the Sertoli-stromal cell tumors, occurred only in the Sertoli component. All 5 LCCSCTs and all other types of sex cord-stromal tumor were negative for β-catenin nuclear staining. In conclusion, SCT-NOS and SSCT frequently show β-catenin nuclear localization. Positive nuclear staining of β-catenin is specific for SCT-NOS, SSCT, and Sertoli-stromal cell tumor among testicular sex cord-stromal tumors but has limited sensitivity (63%) in this group. The similar reactivity of SCT-NOS and SSCT provides additional support that these 2 variants are not distinct entities.