A 41-year-old man with recognized polyostotic fibrous dysplasia since late childhood developed fibroblastic osteogenic sarcoma in the left tibia. Four months after the initial diagnosis, an intramuscular myxoma was discovered in the left thigh. Twenty years previously he had been found to be heterozygous for hemoglobins J(Baltimore) and S. Malignant transformation in fibrous dysplasia is unusual and may be associated in some individuals with prior irradiation. Soft tissue myxomas associated with fibrous dysplasia are even rarer. To the best of the authors' knowledge the occurrence of both of these lesions in a patient with fibrous dysplasia has been reported only once before. Patients with both fibrous dysplasia and myxomas may be at greater risk for malignant transformation than are individuals with only one of these lesions. There is no well-recognized association between hemoglobinopathies and either fibrous dysplasia or bone tumors. It is therefore probable that the rare constellation on findings is in this patient a stochastic event.