Long-lasting intravenous drug abuse causes sclerosis of the superficial venous system. Many drug abusers thus choose to inject into the major veins of the groin or neck. Such practice may, among various other complications, cause deep venous thrombosis. We describe four patients with venous thrombophlebitis localised at the ileo-femoral junction. All patients were intravenous drug abusers, who for many years had injected various drugs into the groin. Two patients suffered a relapse after the treatment was discontinued. One patient had nonfatal pulmonary embolism. All four patients were treated with low-molecular-weight heparin. Three patients were later treated with warfarin, but, owing to bad compliance, this treatment had to be discontinued quite soon in two cases. We conclude that the management of deep venous thrombosis can be difficult in intravenous drug abusers. This is due mainly to poor venous access, the risk of transmitting blood-borne viruses to health personnel, asocial behaviour, and poor compliance. For most patients, we advocate administration of low-molecular-weight heparin for at least three months. Supporting treatment with metadone should be considered in selected cases.