Two hundred and forty-seven phlebograms (113 bilateral and 21 unilateral) were performed in 134 patients 10--14 days after total hip replacement. Fifty-eight per cent of the patients were found to have deep vein thrombosis. The patients with DVT were significantly older than patients without DVT, but there was no difference regarding sex, type of hip prosthesis, side of operation or day of mobilization. No difference was found in the duration of operation and anaesthesia, the operative haemorrhage and the amount of bank blood transfused in patients with and without DVT. Fifty per cent of the thrombi were confined to the calf veins. Ninety-seven per cent of these thrombi were asymptomatic and were as frequent on the operated as on the non-operated side. The remaining 50 per cent of the thrombi engaged the thigh with or without simultaneous calf vein involvement. These thrombi produced symptoms in 23 per cent of the cases and were significantly more common on the operated than on the non-operated side. It is concluded that DVT after hip replacement can be of two different types: thrombosis caused by stasis and the general effects of trauma and thrombosis caused by local factors involving the thigh veins of the operated leg.