While several studies have assessed the efficacy of adrenal fine-needle aspiration, there are few data regarding adrenal tissue core biopsies. We performed a retrospective study, for a 12-year period, of 204 percutaneous adrenal core biopsy specimens. A core was the only specimen obtained, and on-site evaluation was not used. About half of the cases (104/204) were diagnosed as metastatic carcinoma, with lung as the most common origin (78/204). A specificity and sensitivity of 100% for benign vs malignant was calculated, with a specificity of 88% and sensitivity of 86% for specific diagnoses. Diagnostic and sampling errors were identified. False-negatives were limited to biopsies using 20-gauge needles. Cases with a clinical history provided had specific diagnoses made at a slightly higher frequency compared with cases without an available history. Immunohistochemical workup was performed in more than half of the cases; specific diagnoses were made more frequently than in cases without immunostains.