Excessive maternal weight gain during pregnancy can result in serious adverse maternal and neonatal health consequences making it an important outcome to monitor in developing smoking-cessation interventions for pregnant women. Maternal weight gain was investigated in the present study with 154 pregnant participants in controlled trials investigating the efficacy of contingency management (CM) for smoking cessation. Women were assigned to either an abstinence-contingent condition wherein they earned vouchers exchangeable for retail items by abstaining from smoking or to a control condition where they received comparable vouchers independent of smoking status. Mean percent of negative smoking-status tests throughout antepartum was greater in the incentive than control condition (45.2±4.6 vs. 15.5±2.4, p<.001) as was late-pregnancy point-prevalence abstinence (36% vs. 8%, p<.001) but maternal weight gain did not differ significantly between treatment conditions (15.0±0.8kg vs. 15.0±0.9 kg, p=.97). In a comparison of women classified by smoking status rather than treatment condition, a greater percent of negative smoking-status tests predicted significantly more weight gain (0.34 kg per 10% increase in negative tests), an effect that appeared to be attributable to women with greater abstinence having larger infants. This study shows no evidence of excessive maternal weight gain among pregnant women receiving a CM intervention for smoking cessation.