Obesity impacts the physical and psychological health of children and adolescents, and is a risk factor for development of episodic and chronic illness. Rural Mexican-American adolescents are at risk for obesity and associated chronic illnesses.The study used a retrospective chart review of data collected routinely in a rural health clinic setting from 1 January 2005 to 31 December 2010 to assess incidence of overweight/obesity status and episodic or chronic illness among Mexican-American adolescents aged 12–18 years. Analyses included body mass index, age, gender, and episodic or chronic illness diagnoses. Two hundred twelve charts were audited; women (n = 114, 53.8%), men (n = 98 46.2%); normal (n = 105, 49.5%), overweight/obese (n = 107, 50.5%). There were more female normal (n = 61, 53.5%) vs. overweight/obese (n = 53, 46.5%). More male overweight/obese (n = 54, 55.1%) than normal weight (n = 44, 44.9%). Age at first documented overweight/obesity status occurred in early adolescence (median = 13 years, mode = 12 years). Chronic illness incidence was higher among men than women, and overweight/obese vs. normal weight adolescents and in sub-categorizations by weight and specific illness. Incidence of episodic illness was higher among women than men, with variation by weight and specific illness. Disproportionately high incidence of episodic or chronic illness and overweight/obesity identified among rural Mexican-American adolescents compels intervention modification to improve effectiveness.