This study illuminates the associations of body mass index (BMI), socio-economic status (SES), and related behavioral practices including marriage, market visits, and meal consumption among the Tz'utujil Maya of Santiago Atitlán, Guatemala. Semi-structured interviews of 54 adults in Santiago Atitlán were conducted in 2007. The stratified sample was designed to be representative of the seven regional cantones of Santiago Atitlán. BMI was positively associated with years of schooling, income, and literacy, all measures of SES. In addition, BMI was found to be significantly positively correlated with the behavioral practices of marriage, market visits per week, and drinking bottled water. A multiple linear regression model with BMI as the dependent and income, schooling, married, market visits, and bottled water consumption as independent variables is presented and found to be significant. The important behavioral practices highlighted here help to explain how BMI and SES are positively associated, and can inform future public health interventions regarding obesity and malnutrition.