Out of a series of 900 biopsy-proven cases of skeletal "fibroxanthoma" (nonossifying fibroma, fibrous cortical defect), we studied 72 patients with more than one lesion. Age, sex, coexistent conditions such as neurofibromatosis, and histologic and radiographic appearance of the lesions were evaluated. Multiple skeletal fibroxanthomas are probably more common than previously suspected. (At least 8% of the 900 patients in our archives had multiple lesions). Only a small percentage (5%) of patients with multiple skeletal fibroxanthomas had coexistent neurofibromatosis. These lesions are histologically indistinguishable from their solitary counterparts and most commonly present in the lower extremities. Four radiographic patterns were noted: clustered lesions--usually about the knee. nonclustered lesions--in opposite ends of long bones. coalescent lesions--several lesions coalescing over time. This observation has not been previously reported. emergent lesions--lesions appearing in previously unaffected bone. Familiarity with these features may obviate biopsy.