A resistance to the anticoagulant activity of activated protein C (APC), most frequently due to a point mutation in the Factor V gene (the Leiden mutation), represents the most common genetic cause of thrombophilia. The Leiden mutation has been significantly related to pregnancy complications associated with hypercoagulation, e.g. deep vein thrombosis during pregnancy (8-fold increased risk), pre-eclampsia (prevalence of the mutation up to 26%), placental infarction extending to > 10% of the placenta (10-fold increased risk), abruptio placentae (prevalence of the mutation up to 29.6%), and second- and third-trimester pregnancy failure (prevalence of the mutation up to 31.3%). An association of the maternal mutation with recurrent first-trimester miscarriage does not emerge from the literature, although fetal mutation (frequency higher than twice compared with that of the general population) has been related to early spontaneous miscarriage. Although some evidence suggests an association between APC resistance and intrauterine growth retardation, no significant relationship emerges currently from the literature. Screening for the Leiden mutation would seem advisable in women with previous pregnancy complications amongst those associated with APC resistance. Carriers of the mutation should be given appropriate counselling. The screening of asymptomatic women is not recommended at present.