Abstract. Care practices and risk factors for diarrhea among impoverished communities across Mesoamerica are unknown. Using Salud Mesoamérica Initiative baseline data, collected 2011-2013, we assessed the prevalence of diarrhea, adherence to evidence-based treatment guidelines, and potential diarrhea correlates in poor and indigenous communities across Mesoamerica. This study surveyed 14,500 children under 5 years of age in poor areas of El Salvador, Guatemala, Mexico (Chiapas State), Nicaragua, and Panama. We compared diarrhea prevalence and treatment modalities using χ 2 tests and used multivariable Poisson regression models to calculate adjusted risk ratios (aRRs) and 95% confidence intervals (CIs) for potential correlates of diarrhea. The 2-week point prevalence of diarrhea was 13% overall, with significant differences between countries (P < 0.05). Approximately one-third of diarrheal children were given oral rehydration solution and less than 3% were given zinc. Approximately 18% were given much less to drink than usual or nothing to drink at all. Antimotility medication was given to 17% of diarrheal children, while antibiotics were inappropriately given to 36%. In a multivariable regression model, compared with children 0-5 months, those 6-23 months had a 49% increased risk for diarrhea (aRR = 1.49, 95% CI = 1.15, 1.95). Our results call for programs to examine and remedy low adherence to evidence-based treatment guidelines.