Acanthosis nigricans (AN), an entity recognized since the 19th century, is a dermatopathy associated with insulin-resistant conditions, endocrinopathies, drugs, chromosome abnormalities and neoplasia. The latter, also known as malignant AN, is mostly related to abdominal neoplasms. Malignant AN occurs frequently among elderly patients. In these cases, the onset is subtle, and spreading involves the flexural regions of the body, particularly the axillae, palms, soles, and mucosa. Gastric adenocarcinoma is the most frequent associated neoplasia, but many others have been reported. Renal cell carcinoma (RCC), although already reported, is rarely associated with malignant AN. The authors report the case of a woman who was being treated for depression but presented a long-standing and marked weight loss, followed by darkening of the neck and the axillary regions. Physical examination disclosed a tumoral mass in the left flank and symmetrical, pigmented, velvety, verrucous plaques on both axillae, which is classical for AN. The diagnostic work-up disclosed a huge renal mass, which was resected and further diagnosed as a RCC. The post-operative period was uneventful and the skin alteration was evanescent at the first follow-up consultation. The authors call attention to the association of AN with RCC.