This paper introduces the Mater Misericordiae Mothers' Hospital-University of Queensland Study of Pregnancy, a prospective study of 8556 pregnant women interviewed at their first clinic visit, and subsequently interviewed some days after the birth of the baby and again 6 months later. Additional data were derived from the medical record of the pregnancy and delivery. The study was designed to assess the impact of social, psychological and obstetric factors on pregnancy outcome. We present here details of the study design, sampling, response rates and demographic characteristics of the sample.