Idiopathic calcinosis cutis is an uncommon condition characterized by calcium deposits in the dermis, subcutis, and muscles that most commonly are localized in one area. We report the rare case of a 16-year-old adolescent girl who exhibited unusually widespread calcium deposits. The laboratory results showed a normal biochemistry profile. Ultrasonography revealed calcifications in the fat tissue under the skin but not in deeper tissues or muscles. The histopathologic evaluation showed deep cutaneous and subcutaneous calcium deposits. Laboratory investigation revealed normal calcium, phosphate, and parathyroid hormone levels. Calcium excretion in a 24-hour urine sample was normal, but phosphate excretion was slightly low. Scintigraphic research showed no pathology in the thyroid and parathyroid glands but revealed soft-tissue calcification. A chest roentgenogram, blood tests, and testing of stools for occult blood showed no indication of internal malignancy. On the basis of these findings,the diagnosis of idiopathic calcinosis cutis was made. We discuss the pathogenesis, clinical and histologic picture, and differential diagnosis of calcinosis cutis.