GATA-3 expression in testicular/gynecologic mesothelial neoplasms and benign mesothelia have not been completely investigated. We graded GATA-3, calretinin, and WT1 staining in 20 adenomatoid tumors [9/20 (para)testicular and 11/20 tubal/uterine] and 38 normal mesothelia (20/38 tunica vaginalis and 18/38 fallopian tubes) as either 0 (≤5%), +1 (>5% and <25%), +2 (≥25% and ≤50%), and +3 (>50%). Adenomatoid tumor GATA-3 staining: 2 urologic cases were positive (2/9, +3 and +1), no gynecologic cases were positive (0/11), and all were positive for WT1/calretinin (20/20,+2 to +3). The normal tunica vaginalis mesothelia: 3 of 20 were GATA-3 positive (+2) while 20 of 20 were WT1/calretinin (+2 to +3) positive. The gynecologic cases with walthard nests: are positive for GATA-3 (18/18,+3), WT1 (11/18, +2 to +3), and calretinin (1/18,+2). The nonmetaplastic gynecologic mesothelia were GATA-3 negative (18/18) and WT1/calretinin postive (18/18,+2 to +3). All 18 epididymi were GATA-3 positive (+3) and negative for WT1/calretinin. All 11 efferent ductules examined were negative for GATA-3, WT1/calretinin (0/11). Although GATA-3 rarely stains adenomatoid tumors, gynecologic walthard nests are consistently positive with GATA-3 staining but lose mesothelial markers reflecting a metaplastic change. Excluding the walthard nests, GATA-3 is rarely positive in normal urologic and gynecologic mesothelia. GATA-3 is uniformally positive in epididymi and negative in efferent ductules, which may be due to their embryological evolvement. Awareness of the GATA-3 staining patterns in the genitourinary and gynecologic mesothelial tissues and their respective neoplasms is important to prevent misdiagnosis and possible unnecessary interventions.