Antiphospholipid antibodies (APA), lupus anticoagulant (LA) and/or anticardiolipin antibodies (ACA), are associated with thrombosis and recurrent miscarriage. We studied the outcome of 20 pregnancies in women (median age 32 years; range 23-41) with APA (14 LA positive; three immunoglobulin (Ig) G ACA positive; two IgM ACA positive and one LA and IgG ACA positive) and history of recurrent miscarriage (median 4; range 3-11) who declined pharmacological treatment in their next pregnancy. Comparison was made with a cohort of 100 consecutive women (median age 33 years; range 23-44) with recurrent miscarriage (median 4; range 3-10), in whom no underlying cause to account for their pregnancy losses was found. Of the 20 women with APA, 18 (90%) miscarried compared to 34 of the 100 women (34%) with normal investigations (P < 0.001). The majority (94%) of miscarriages in women with APA occurred in the first trimester. Fetal heart activity was seen prior to fetal death in 86% of women with APA compared to 43% of women with normal investigations (P < 0.01). The first trimester loss of embryonic pregnancies is the most common type of miscarriage in women with APA. This may be a result of defective implantation and subsequent placentation.