Superovulation therapy during assisted conception may result in a hypercoagulable state. Five cases of upper extremity venous thrombosis were identified in women who conceived after ovarian stimulation for in vitro fertilization (IVF). They presented between 7 and 10 weeks' gestation with neck pain and swelling. Three had been treated for ovarian hyperstimulation syndrome and two had evidence of inherited thrombophilia. Four patients received thromboprophylaxis before presentation. Although thrombosis is an uncommon complication of IVF, patients should be counselled before treatment. Thrombophilia screening may be considered for 'high-risk' patients, although current regimes for thromboprophylaxis remain suboptimal.