Summary A case of polyostotic fibrous dysplasia in a 5-year-old girl is reported. The diagnosis was made by the characteristic triad of predominantly unilateral bone lesions, precocious “puberty,” and unilateral skin pigmentation, and was substantiated by radiographic and pathologic examination of the bone lesions. The early onset of menses (second day of life) is somewhat unusual as is the contralateral distribution of skin pigmentation. The differential diagnosis is discussed briefly.