A case is reported of spinal subarachnoid haematoma occurring after spinal anaesthesia. The patient was given prophylactic pre and postoperative low molecular weight heparin. On the second postoperative day, he complained of backache and got a partial cauda equina syndrome. Magnetic resonance imaging carried out on the 6th day confirmed the presence of a spinal haematoma, which was removed surgically. One year later, the bilateral motor palsy which had involved several roots, had completely regressed. It remained a severe sensory loss associated with a loss of sphincter control. This case highlights the role of predisposing factors and the importance of early diagnosis.