A case of advanced leiomyosarcoma of the urinary bladder is reported in a 25-year old man who, in a short time, experienced a complete 'spontaneous' regression of his fatal illness. He first presented with severe haemoperitoneum resulting from an unresectable bleeding tumour of the urinary bladder. Debulking surgery was performed, followed by salvage chemotherapy. Histological and ultrastructural examinations of the tumour confirmed a poorly differentiated leiomyosarcoma. The residual disease failed to respond to salvage chemotherapy, but regressed 'spontaneously' 5 months after cessation of therapy. The patient is alive without evidence of disease 51 months after the diagnosis. This remarkable phenomenon and relatively long survival in a poor-risk leiomyosarcoma of the urinary bladder has never been reported previously.