Excess gestational weight gain (GWG) contributes to long-term obesity in mothers and children. To guide the tailoring of interventions to prevent excess GWG, a better understanding is needed of the lifestyle-related health cognitions that influence women's attempts to manage GWG.To examine the relationship between health cognitions and excess GWG for women who enter pregnancy at a healthy weight (body mass index <25) or overweight (body mass index ≥25). It was hypothesized that health cognitions with a positive (negative) influence on health behavior would be associated with lower (higher) likelihood of excess GWG and that specific associations would differ between weight status groups.This prospective, observational study commenced when participants were <20 weeks' gestation, continuing until the end of their pregnancy. A self-administered quantitative survey at recruitment assessed prepregnancy weight and lifestyle-related health cognitions. Height was measured at 16 weeks and weight at 36 weeks using standard procedures.A consecutive sample of pregnant women (n=715) were recruited from an Australian metropolitan hospital between August 2010 and January 2011. All women <20 weeks' gestation were eligible unless they had preexisting type 1 or 2 diabetes or insufficient English language skills to complete questionnaires.Excess GWG defined according to Institute of Medicine 2009 recommendations and predisposing, reinforcing, and enabling cognitions for lifestyle health behaviors.Logistic regression analyses examined associations between health cognitions and excess GWG stratified for prepregnancy weight status.For healthy-weight women, higher weight locus of control scores were protective against excess GWG (odds ratio 0.6, 95% CI 0.4 to 0.8), whereas higher perceived risk scores (personal risk and risk arising from prepregnancy weight) (odds ratio 1.3, 95% CI 1.1 to 1.7) were associated with excess GWG. For overweight women higher negative outcome expectation scores were associated with an increased risk of excess GWG (odds ratio 1.4, 95% CI 1.1 to 2.0).Lifestyle-related health cognitions are associated with excess GWG and differed by prepregnancy weight status, suggesting the need to tailor behavior change interventions accordingly.