Many factors interact to create barriers to dietary and exercise plan adherence among medically underserved patients with chronic disease, but aspects related to culture and ethnicity are underexamined in the literature. Using both qualitative (n = 71) and quantitative (n = 297) data collected in a 4-year, multimethod study among patients with hypertension and/or diabetes, the authors explored differences in self-reported adherence to diet and exercise plans and self-reported daily diet and exercise practices across four ethnic groups—Whites, Blacks, Vietnamese, and Latinos—at a primary health care center in Massachusetts. Adherence to diet and exercise plans differed across ethnic groups even after controlling for key sociodemographic variables, with Vietnamese participants reporting the highest adherence. Food and exercise options were shaped by economic constraints as well as ethnic and cultural familiarity with certain foods and types of activity. These findings indicate that health care providers should consider ethnicity and economic status together to increase effectiveness in encouraging diverse populations with chronic disease to make healthy lifestyle changes.