Whether or not pregnant women with a previous episode of venous thromboembolism (VTE) should receive antithrombotic prophylaxis is a matter of debate. In order to estimate the rate of recurrent deep venous thrombosis (DVT) or pulmonary embolism (PE) during pregnancy and puerperium we retrospectively investigated a cohort of 1104 women with previous VTE; after a single DVT or isolated PE, 88 of them became pregnant at least once without receiving antithrombotic prophylaxis. Overall, 155 pregnancies and 120 puerperium periods without prophylaxis were recorded. There were nine recurrences during pregnancy and 10 during puerperium, with a rate of 5·8% [95% confidence interval (CI) 3·0–10·6] and 8·3% (95%CI 4·5–14·6) respectively. In pregnancy, the rate of recurrence was 7·5% (95%CI 4·0–13·7) if the first VTE was unprovoked, related to pregnancy or to oral contraceptive use, whereas no recurrence occurred if the first VTE was related to other transient risk factors. In puerperium, the rate of recurrence was 15·5% (95%CI 7·7–28·7) in women with a pregnancy-related first VTE, with a risk 3·9-times higher than in the remaining women. Inherited thrombophilia was not associated with a statistically significant increase in risk of recurrence in pregnancy or in puerperium, yet the rate of recurrence in puerperium was 14·2% (95%CI 5·7–31·4) in overall carriers of factor V Leiden and 30% (95%CI 10·7–60·3) in carriers with a pregnancy-related first VTE, with a risk 6·8 times higher than in women without thrombophilia and with a non pregnancy-related first VTE.