The aims of this thesis were to determine the incidence and risks of deep venous thrombosis (DVT) in the general population and in vascular surgery. The long-term outcome after DVT was also evaluated.

The incidence and risks of DVT in the general population were studied in a population-based questionnaire survey in years 1989 and 1994. A questionnaire was sent to all residents of Tampere born 1929, 1939 and 1949. Items included questions related to previous diseases, medication and symptoms in legs. In the first questionnaire the number of respondents was 5568, in the the second five years later 4903 (participation rates were 83-88%). The incidence and risks of postoperative DVT were studied in the nationwide FINNVASC registry (a total of 7533 procedures during years 1991-1992).

Outcome of DVT was studied 5 or 10 years after the acute phase in 70 patients. A questionnaire was used to get information on leg symptoms and their severity, visits to medical health care centres and the use of compression stockings. 26 patients were followed up for two years. Control studies included ultrasonographic examinations 7 and 20 months after DVT and contrast phlebography 7 months after DVT. Leh symptoms at the end of the follow-up were evaluated by means of a questionnaire.

This thesis showed that the incidence of deep venous thrombosis in the general Finnish population is approximately 140 per 100 000 annually. DVT seemed to be associated with pre-existing varicose veins and sex-steroid therapy. The incidence of DVT in patients undergoing vascular procedures was low (0.45%). The majority of postoperative DVTs were diagnosed in patients undergoing operations on the aorta or the lower limb.

The long-term symptoms were frequently reported in legs with previous deep venous thrombosis. In a 2-year follow-up the amount of asymptomatic patients was 27% and in the longer follow-up period 13%. There was no difference in the development of symptoms after DVT between calf and more proximal DVT. Radiological studies revealed that the thrombus opened almost in all cases (93%), but the pathologic findings in the popliteal veins were commonly noted.

Deep venous thrombosis was relatively common among middle-aged people in Finland. The incidence of DVT was within the range estimated in previous studies in industrialized countries. The association between varicose veins and DVT was interesting and needs to be studied in the future. Symptoms in legs with previous DVT were common. The initial site of an acute DVT did not associate with late symptoms. Late involvement in popliteal vein was noted in some patients after calf DVT.