Medical problems account for almost 50% of all maternal deaths in South Africa. The most recent report of the National Committee on Confidential Enquiries into Maternal Deaths (NCCEMD) (2008 - 2010) stated that 40.5% of deaths were due to non-pregnancy-related infections, which are mostly HIV-related, and 8.8% were due to medical or surgical disorders. Obstetric physicians have a specific role in managing pregnant and postpartum women with medical problems and, in partnership with obstetricians, can contribute to reducing maternal morbidity and mortality. There are physiological changes in almost all systems in pregnancy. For example, changes in the cardiovascular, respiratory and haematological systems are particularly important when assessing the cause and management of medical problems in pregnant women. Such problems may be unique to pregnancy, exacerbated by pregnancy, or unrelated to pregnancy. They may be present prior to pregnancy, or present for the first time in pregnancy. Some medical problems are worsened by pregnancy. Pregnant women may improve or remain stable, or their disease may predictably or unpredictably deteriorate. This article discusses the role of obstetric physicians in managing medical problems in pregnant women. A case is described of a pregnant woman with common medical problems, resulting in a serious complication when treatment is interrupted.