A series of 161 hydronephrotic kidneys from a 30-year period in 147 children is reported. The left kidney was affected more frequently than the right and the condition was more common in the male than in the female child. In infants, abdominal mass was a common mode of presentation. In older children, loin or abdominal pain, haematuria and urinary tract infection were typical findings. The principles of treatment have changed: during 3 decades there has been a definite shift from nephrectomy to dismembered pyeloplasty, mostly according to Anderson-Hynes technique or its modifications. The results of the dismembered pyeloplasties were good or excellent as contrasted with often unsatisfactory results of the non-dismembered pyeloplasties. There were 1 early and 1 late death in the series; both of these patients were uraemic already preoperatively. The key to good results is the dismembered pyeloplasty with postoperative nephrostomy drainage and applying a stent for the anastomosis, combined with strict control of postoperative pyelonephritis.