A case of Gorham's disease involving the proximal femur of a 12-year-old girl is presented. Although Gorham's disease is rare and has benign histologic characteristics, in this patient it took an aggressive clinical course that resulted in severe morbidity. Diagnosis is difficult to establish; almost all investigative approaches provide only indirect evidence of the pathology. A high index of suspicion and open biopsy performed soon after presentation will establish diagnosis. Treatment modalities may be more effective if applied earlier in the disease process, especially as the osteolytic process appears to escalate after pathologic fractures, which occur frequently in this disorder.