PURPOSE: While treating 14 phenylketonuria(PKU) patients, we evaluated bone density, changes in bone age, andbony changes such as spiculation or metaphyseal widening. MATERIALS AND METHODS: A total of 14 PKU patients agedbetween 1 month and 14 years(mean, 6.4 years) were under dietary treatment. Eight and eleven patients underwentradiography of the left hand and wrist and bone densitometry(BMD) of the lumbar spine, respectively. The resultswere reviewed with regard to abnormal bony changes, delayed bone age, and osteopenia. Patients were assigned toeither the early or late treatment group, depending on whether or not dietary therapy was started before 3 monthsof age. Those in whom a blood phenylalanine level of under 10 mg/dl was maintained were assigned to the 'goodcontrol' group; others were classified as 'variable control'. The findings of radiographs of the left hand andlumbar BMD were evaluated in relation to the time of dietary therapy, and adequacy of treatment. RESULTS: Onlumbar BMD, four of 11 patients (36%) showed reduced bone density of more than 1 S.D. None of the 11 who underwentradiography of the left hand showed bony abnormalities such as spiculation or metaphyseal widening. In four of the11, bone age was less than chronological age by at least one year. According to Fisher's exact test there was norelation between delayed bone age , osteoporosis and the time and adequacy of dietary therapy (p >0.05). CONCLUSION: None of the 14 PKU patients who underwent dietary therapy had bony abnormalities such as spiculationor metaphyseal widening. In four of the 11, bone age was at least one year less than chronological age, and onlumbar BMD, osteoporosis was seen. For the evaluation of bone change in PKU patients, plain radiography and BMDare thus complementary.