Thirteen patients who had undergone prolonged adrenocorticotropic hormone (ACTH) therapy for infantile spasms or myoclonic encephalopathy were examined with sonography. Nine patients were found to have appearances characteristic of medullary nephrocalcinosis. In each of these infants the cortical echogenicity was normal in the presence of focal areas of increased echogenicity within the renal pyramids. Five patients also showed a homogeneously increased echogenicity of the whole pancreas on sonography, and two of these showed increased density on computed tomography. Density measurements were in the range of calcific material within the papillae and pancreatic tissue. On abdominal survey radiographs, even in retrospect no calcifications could be recognized.