BACKGROUND: The use of complementary and alternative medicine (CAM) has become increasingly prevalent in industrialised countries, with women being the most prolific users. Some women continue to consume these therapies when they become pregnant. AIM: To review the literature exploring prevalence and motivation for use of complementary and alternative medicine by pregnant women. METHOD: A search for relevant literature published from 2001 was undertaken using a range of databases and by examining relevant bibliographies. RESULTS: Although the estimates vary widely from 1% to 87%, the general trend indicates that a significant number of pregnant women use complementary and alternative medicine. Common modalities used include massage, vitamin and mineral supplements, herbal medicine, relaxation therapies and aromatherapy. Reasons for use are varied and include the belief that these therapies offer safe alternatives to pharmaceuticals, they allow greater choice and control over the childbearing experiences, and they are congruent with their holistic health beliefs. The influence of traditional cultural practices on the use of these therapies is unclear. Most expectant women rely on advice from family and friends, and many do not disclose their use to their pregnancy care providers. CONCLUSIONS: Many women use complementary and alternative medicine when they are pregnant. Further research is needed to gain a greater understanding of the true prevalence and expectant women's motivation for the use of complementary and alternative medicine. Health-care professionals are encouraged to ask women about their use of these treatments and seek out relevant information.