Two patients presented with macroscopic haematuria and dysuria. Cytoscopic examination showed haemorrhagic cystitis. The findings of casts in the urine and of impaired renal function led to renal biopsies. These showed glomerulonephritis with deposits of IgA in the mesangium. No evidence of viral infection was found. A third patient diagnosed on biopsy 9 years previously as having focal glomerulonephritis developed gross haematuria and dysuria. Cystoscopy revealed haemorrhagic cystitis, and deposits of immunoglobulins were present in the bladder wall. It is suggested that haemorrhagic cystitis may occur as part of a syndrome with glomerulonephritis and may be due to an immunological mechanism.