Concern about the risks of cardiovascular illness in women using combined oral contraceptives (OC) containing the progestagens desogestrel and gestodene prompted two studies of data from the UK General Practice Research Database. We compared the risks of certain cardiovascular illnesses in otherwise healthy women exposed to one of three OCs containing < 35 micrograms oestrogen plus levonorgestrel, desogestrel, or gestodene. In the first study, based on some 470 general practices, there were 15 cases of unexpected idiopathic cardiovascular death among 303,470 women who were current users of one of the study OCs. The estimated incidence rates were 8/184,536 (4.3 per 100,000) woman-years at risk for users of combined OCs containing levonorgestrel, 2/135,567 (1.5 per 100,000) for desogestrel users, and 5/105,201 (4.8 per 100,000) for gestodene users. The relative risk (RR) estimates were 0.4 (95% CI 0.1-2.1) and 1.4 (CI 0.5-4.5) for desogestrel and gestodene, respectively, compared with levonorgestrel. In the second study, derived from some 370 general practices, there were 80 cases of nonfatal venous thromboembolism (VTE) in a cohort of 238,130 otherwise healthy women. The incidence rates of VTE per 100,000 woman-years at risk were 16.1 for levonorgestrel users, 29.3 for desogestrel, and 28.1 for gestodene. The adjusted RR estimates from the cohort analysis were 1.9 (1.1-3.2) and 1.8 (1.0-3.2) for desogestrel and gestodene users, respectively, compared with users of levonorgestrel. In a nested case-control analysis the adjusted matched RR estimates were 2.2 (1.1-4.4) and 2.1 (1.0-4.4) for desogestrel and gestodene users, respectively, compared with users of levonorgestrel. The excess risk for nonfatal VTE associated with the new generation of combined OCs containing low-dose oestrogen and the progestagens desogestrel or gestodene compared with levonorgestrel is estimated to be 16 per 100,000 woman-years.