We describe 2 young patients with severe cerebrovascular thrombotic events whose only risk factor was intake of oral contraceptives. A 41-year-old woman suffered thrombosis of the basilar artery and remained disabled with a locked-in syndrome; a 23-year-old woman had thrombosis of the sinus sagittalis. These 2 cases and the current discussion regarding the use of hormones either as oral contraceptives or hormonal replacement therapy with estrogens and/or progestins prompted a review of the literature and a review of all spontaneous reports from 1991 to 1995 to SANZ (Schweizerische Arzneimittel-Nebenwirkungs-Zentrale), the Swiss Drug Side Effects Monitoring Center. The spontaneous reporting under this system does not allow conclusions on prevalence and incidence of adverse events. In these 5 years 33 vascular events associated with different hormones were reported. There were 28 reports of venous thrombosis of the lower and upper limb or pulmonary embolisms, and 5 reports of cerebrovascular complications. In 9 of 33 cases the hormones were used as hormonal replacement therapy and in 24 of 33 cases as oral contraceptives. In half of these women other risk factors for thromboembolic events such as overweight, family history of thrombosis and immobilization were known. Complications occurred with different preparations containing different estrogens and progestins. According to the literature, third generation progestins seem to involve a slightly increased risk of venous thromboembolism but a reduced risk of arterial thromboembolic events, which was confirmed by the SANZ data (17 of all 24 cases). Increasing age and rising estrogen dosage of oral contraceptives are associated with increased risk of vascular events. Although thromboembolic events also occur during hormonal replacement therapy with naturally occurring estrogens, the prophylactic potential of these drugs with regard to osteoporosis and cardiovascular events certainly outweighs this risk.