Objective To investigate the association between birth outcomes and blood levels of aflatoxin B1 (AFB1)-lysine adduct in pregnant women in Kumasi, Ghana. Method A cross-sectional study of 785 pregnant women attending antenatal clinic was conducted. Aflatoxin B1 (AFB1)-lysine adduct levels were determined by high performance liquid chromatography (HPLC) on blood taken after delivery. The birth outcomes considered were small for gestation age, low birthweight, preterm delivery and stillbirth. Participants were divided into quartiles based on the distribution of aflatoxin B 1-lysine adducts in pg/mg albumin ('low': ≤2.67, 'moderate': >2.67 to ≤4.97, 'high': >4.97 to ≤11.34, 'very high': >11.34). Statistical analysis involved models that included socio-demographic variables and other potential confounders. Results The average AFB1-lysine adduct level in maternal serum was 10.9 ± 19.00 pg/mg albumin (range = 0.44-268.73 pg/mg). After adjusting for socio-demographic variables and potential confounding factors, participants in the highest AFB 1-lysine quartile with 'very high' AFB1-lysine level (>11.34 pg/mg) were more likely to have low birthweight babies (OR, 2.09; 95% CI, 1.19-3.68), and showed a trend of increasing risk for low birthweight (Ptrend = 0.007) compared to participants in the lowest quartile. Conclusion This study adds to the growing body of evidence that aflatoxins may increase the risk of adverse birth outcomes. The findings have implications for targeted nutritional education of pregnant women in areas with high levels of aflatoxin contamination of foods. © 2009 Blackwell Publishing Ltd.