Acne is one of the most common skin diseases in the general population, especially among adolescents. Acne tarda (adult acne) is defined as acne that develops (late-onset acne) or continues (persistent acne) after 25 years of age. The disease is more common in women. The clinical features are quite specific: inflammatory acne in the lower facial region or macrocomedones (microcysts) spread over the face. Involvement of the trunk is much more common in men. The etiology of acne tarda is still controversial, as cosmetics, drugs, smoking, stress, diet, and endocrine abnormalities have been implicated. Women with acne tarda and other symptoms of hyperandrogenism have a high probability of endocrine abnormalities such as polycystic ovary syndrome. Treatment is similar to that of acne in adolescence. Long-term treatment over years or decades may be required.