Multi-centre trial involving 46 hospitals in the United Kingdom, with patients entered by 137 Consultant Physicians. Consenting patients were randomised in a central office to either 3 months' or 6 months' anticoagulation. Information on progress of the patients was requested by the co-ordinating office at 3 months, 6 months and 12 months. Outcomes were measured as death from DVT/PE, non-fatal extensions or recurrences of DVT/PE and major haemorrhages during and after anticoagulation.