Lower socioeconomic status (SES) is consistently associated with adverse pregnancy outcomes. One mechanism that may account for this association is that maternal health behaviors vary with SES. To examine this possibility, we addressed how women may be differently categorized by diverse measures of SES and the effect that choice of measure has on the relationship between SES and maternal health behaviors. We used population-based data for Caucasian women (n = 10,055) from Alaska, Maine, Oklahoma, and West Virginia who delivered a live infant in 1990-1991 and participated in the Pregnancy Risk Assessment Monitoring System. Five SES measures were evaluated: education; poverty status; Medicaid payment for delivery; Women, Infants, and Children (WIC) enrollment during pregnancy; and residential crowding. Three maternal health behaviors (smoking, delayed/no prenatal care, unintended pregnancy) were examined to assess the variation among the associations between SES measures and behaviors. Item response rates were high for all SES measures (range: 88.9%-100.0%), and there was low correlation between measures. Most of the SES measures were related to maternal health behaviors. However, the strength of association varied between each measure and behavior and was weaker for women who were younger than 20 years old or not married. In view of the multifaceted nature of SES, several measures may be needed to appropriately assess the relationship between SES and maternal health behaviors.