Osteoma cutis (osteosis cutis, osteosis cutis multiplex) is a more common complication in acne than the less than 50 publications suggest. It is usually subclinical, showing up on X-ray examination in as many as 5%–10% of patients with persistent inflammatory acne. When (rarely) clinically apparent, ectopic bone formation can present baffling diagnostic problems. Osteoma cutis occurs as small, skin-colored, dome-shaped papules, 1–2 mm in diameter. Usually they are numerous, sometimes up to several hundred. They do not progess or regress, being permanent. Osteoma cutis favors the face but sometimes develops on the neck and on the chest. The nodules are rock-hard, painless, and noninflamed.