In 2006, the city of Milwaukee ranked worse than any Wisconsin county for health outcomes and worse than all but 1 county for health determinants.To further examine disparities in health, Milwaukee city ZIP codes were stratified into 3 groups (lower, middle, and upper) by socioeconomic status (SES). Health determinants (15 measures) and health outcomes (2 measures) were compared across these ZIP code groups, and to the rest of Wisconsin.The risk ratio for the lower SES group in comparison to the upper SES group was at least 2.0 for 5 of the 17 measures examined, and was at least 1.5 for 13 of the 17 measures. The upper SES group in Milwaukee, while the healthiest in the city, was worse than the state average in 6 measures.Large health disparities within the city of Milwaukee are associated with geographic regions of differing socioeconomic status. As the state's largest urban center, Milwaukee's relatively poor health and significant health disparities have a considerable impact on the overall health of the state. To improve population health in Wisconsin, substantial efforts and resources are needed to address these disparities, and their related upstream factors.