A 10-year-old boy, in a precomatose state, was admitted to our Endocrine Unit for diabetic ketoacidosis. It took unusually long to reequilibrate the acidosis despite a bicarbonate drip. On the 4th day the patient suddenly complained of an acute abdominal pain associated with macrohematuria and oliguria; ankle edema was evident. No radio-opaque image was detected along the urinary tract. An intravenous pyelogram (IVP) showed an almost totally silent left kidney. Ten days later a control IVP showed complete normality of both kidneys. We postulated that the serious and protracted dehydration might have resulted in the formation of a blood clot along the renal tract and that the rehydration may have subsequently removed it.