There is some evidence that postoperative deep vein thrombosis (DVT) may be commoner in cool than in warm climates. To determine whether this complication is less common in the subtropical climate of Brisbane than in more temperate locations, the incidence of DVT after major abdominal surgery was assessed by 125I fibrinogen scanning. In order to avoid overestimating the incidence of DVT, abnormal scans were accepted as diagnostic only if the DVT was confirmed by venography or if the abnormality on the scan fulfilled more stringent criteria than have previously been applied. Thirty-six of 152 patients (24 per cent) developed a DVT; this incidence was significantly lower than in one previous study from Melbourne and higher than that found in South-East Asia and East Africa, but was not significantly different from that reported from Sydney, Japan and several centres in North America and Britain. There was no apparent seasonal variation in the incidence of the complication. The geographical variation in incidence of postoperative DVT may have been overestimated in previous reports and may be at least partly due to variations in screening technique.