A 14-year-old boy undergoing treatment for nephrotic syndrome with steroids and cyclosporine presented with small sclerotic bone lesions in a routine chest radiograph. Similar lesions were found in other bones of the axial and appendicular skeleton. Despite the paucity of clinical symptoms and absence of laboratory data suggesting systemic mastocytosis, the diagnosis of an indolent form of this disorder was made based on radiographic signs and confirmed by biopsy.