One hundred and thirty three children were studied (a total of 218 scintigrams) after IV injection of 100 microCi/kg 99Tc-MDP. Of 64 pathological hips (6 being bilateral), 52 were judged typically abnormal, 8 without initial radiological evidence. Of the rest, 8 were considered doubtful and 4 normal. No scan was considered typical of Perthes' disease in other hip disorders. The resulting figure of the sensitivity was 94%, for specificity 97%, for positive predictive value 97%, and for negative predictive value 95%. It is more difficult to assess the value of bone scintigraphy in the follow up of these patients. The disappearance of uptake defect in the femoral head may be a good index and occurs earlier than the normalization of the radiographs. On the other hand, the significance of the neighbouring region of increased uptake is difficult to assess although related to revascularization and reconstruction. The evolution of the disease does not seem to be correlated with the localization and the intensity of these regions in a straightforward manner.