Abstract Background Smoking and obesity are associated with adverse pregnancy outcomes. The aim of the present study was to examine the association between smoking, obesity (BMI > 30), and risk for venous thromboembolism (VTE) during pregnancy and the puerperium. Materials and methods In a population-based case-control study nested within a Danish cohort of 71,729 women, we identified 129 cases with VTE in pregnancy or the puerperium, and 258 pregnant non-VTE controls. We obtained data from medical records regarding current smoking status, BMI, and other covariates, and computed the odds ratios (OR) for VTE as a measure of relative risk. Results Smoking and obesity were associated with increased risk of VTE during pregnancy and the puerperium (adjusted OR 2.7 (95% CI: 1.5, 4.9) and 5.3 (95% CI: 2.1, 13.5), respectively). Obesity appeared to be associated with a higher risk of pulmonary embolism (adjusted OR: 14.9 (95% CI: 3.0, 74.8) than of deep venous thrombosis (adjusted OR: 4.4, 95% CI: 1.6, 11.9). Conclusion Smoking and obesity are risk factors for VTE in pregnancy and the puerperium.