Epidemiologic evidence provides some support for a causal association between maternal secondhand smoke (SHS) exposure during pregnancy and reduction in infant birth weight. The purpose of this cross-sectional study is to examine the magnitude of this association in China, where both prevalence and dose of SHS exposure are thought to be higher than in U.S. populations. Women who gave birth in Beijing and Changchun September 2000–November 2001 were interviewed to quantify self-reported prenatal SHS exposure. Their medical records were reviewed for data on pregnancy complications and birth outcomes. Non-smoking women who delivered term babies (≥37 weeks gestation) were included in the study (N = 2,770). Nearly a quarter of the women (24%) reported daily SHS exposure, 47% reported no prenatal exposure, and 75% denied any SHS exposure from the husband smoking at home. Overall, no deficit in mean birth weight was observed with exposure from all sources of SHS combined (+11 grams, 95% CI: +2, +21). Infants had higher mean birth weights among the exposed than the unexposed for all measures of SHS exposure. Future studies on SHS exposure and infant birth weight in China should emphasize more objective measures of exposure to quantify and account for any exposure misclassification. Full article