We report the clinicopathologic, immunophenotypic, DNA ploidy, and MIB-1 proliferative findings of five adenomatoid tumors of the adrenal gland. All patients were male, and tumors were incidental radiologic, surgical, or autopsy findings. Mean patient age at diagnosis was 41 years (range 31-64 years). The tumors ranged from 1.2 to 3.5 cm (mean 2.8 cm; median 3.2 cm) in greatest dimension, and all originated within the adrenal gland. The tumors were composed of anastomosing variably sized tubules lined by epithelioid as well as flattened cells. Signet-ring-like cells were present in all cases. The previously described histologic patterns of adenomatoid tumor, adenoid, angiomatoid, cystic, and solid, were observed, and each tumor contained multiple histologic patterns. In three of five cases, there was extra-adrenal extension of tumor into periadrenal adipose tissue. All adenomatoid tumors infiltrated the adrenal cortex, and in four cases the adrenal medulla was involved. All tumors exhibited strong immunoreactivity for calretinin, cytokeratins AE1/AE3, and CAM 5.2, cytokeratin 7, and vimentin. Tumors showed weak and focal immunoreactivity for cytokeratin 5/cytokeratin 6 and were negative for CD15, CD31, CD34, cytokeratin 20, MOC31, and polyclonal carcinoembryonic antigen. Ploidy analysis using Feulgen-stained sections and image analysis showed that three tumors were diploid and two were tetraploid. Tumors exhibited low MIB-1 proliferative activity, ranging from 0.2% to 2.7% (mean 1.6%). In three cases with clinical follow-up, no recurrence or metastases occurred. Adrenal gland adenomatoid tumors are morphologically and immunophenotypically identical to adenomatoid tumors of the genital tract and appear benign.