A previously well 42-year-old man presented with a three-hour history of pain in the right flank of acute onset. At laparotomy he was found to have a ruptured right kidney which was treated by nephrectomy. Eight days later he developed similar symptoms on the left: at operation 21 of blood were drained and nephrostomy and catheterisation carried out. He recovered after a complicated postoperative course, and histological examination of the removed kidney, and biopsy specimens, showed classic polyarteritis nodosa. This is a rare cause of spontaneous rupture of the kidney but must be considered whenever a patient presents with renal haemorrhage of unknown cause.