Introduction Adverse outcomes of pregnancy are global health problems that are much more pronounced in developing countries. The risk factors associated with adverse outcomes of pregnancy are multifactorial. In South Africa, the population prevalence and associated risk factors of maternal and perinatal mortality are routinely documented, but there are gaps in the data on other pregnancy adverse outcomes. This study was aimed at determining the prevalence rates and related risk factors of preterm births and pregnancy loss in an urban population in South Africa. Methods The study was a cross-sectional analytical community study of women 18 to 49 years of age, living in the Potchefstroom municipality. It was conducted from August 2007 to April 2008. Participants were selected using a systematic random sampling strategy; 1 210 women participated. An adapted reproductive health questionnaire was used to collect sociodemographic, environmental, occupational and reproductive health data. Results Prevalence of pregnancy loss and preterm births were estimated to be 5.6% [95% CI: 5.57% - 5.63%] and 13.4% [95% CI: 13.36% - 13.44%], respectively. Pregnancy loss was associated with psychological stress and working during pregnancy; preterm birth was associated with White, Coloured and Indian race, primary and high school education, psychological stress and chronic disease; and antenatal care use was protective against both pregnancy loss and preterm birth. Conclusion The prevalence of pregnancy loss found in this study was lower than would be expected in the general South African population; while the preterm birth prevalence, although lower than that of other developing and middle income countries, could be improved. Generally, there are common risk factors for pregnancy loss and for preterm births. Some of the existing evidence on risk factors was supported by the findings of this study. Improvement of surveillance and health information systems for pregnancy loss and preterm births would provide essential information on the burden of these outcomes in South Africa and would subsequently guide policy, research and prioritisation of effective control programmes