AIMS To determine risk factors for miscarriage. METHODS A case control study was carried out at the gynaecological wards and antenatal clinics of the De Soysa Maternity Hospital in Sri Lanka. A case was defined as that of mothers with a confirmed diagnosis of partial or full expulsion of the fetus during the first 28 weeks of gestation. Controls comprised ante-natal clinic attendees whose period of gestation was <28 weeks and carrying a viable fetus. Two hundred and thirty cases and 504 controls were selected. A pre-tested interviewer-administered questionnaire and modified life events inventory were used to gather data. Multivariate logistic regression was applied separately for first and second trimester miscarriages and the results were expressed as odds ratios (OR) and as 95% confidence intervals (95% CI). RESULTS Sleeping < or =8 h/day (OR:3.80, 95% CI:1.01-14.3) was found to be a risk factor for first trimester miscarriage controlling for the effect of period of gestation. Sleeping < or =8 h/day (OR:2.04, 95% CI:1.24-3.37), standing < or =3 h/day (OR:1.83, 95% CI:1.08-3.10), exposure to cooking smoke (OR:3.83, 95% CI:1.50-9.90) and physical trauma during the pregnancy (OR:43.2, 95% CI:4.55-411.4) were found to be risk factors for second trimester miscarriage controlling for the effect of period of gestation. CONCLUSIONS Sleep deprivation, a sedentary lifestyle, exposure to cooking smoke and physical trauma during pregnancy were risk factors for miscarriage. Most of the risk factors are therefore modifiable.