Background: Acute Respiratory Infection (ARI) is still one of the health problems in developed and developing countries including Indonesia. ARI is the most common disease in outpatients in North Sumatra, especially in Medan. This study aims to find out about the factors that influence ARI in toddlers in Simalingkar Health Center Medan, including nutritional status, birth weight, history of immunization, exclusive breastfeeding, and parental smoking status. Subjects and Method: This was a cross sectional study. The sample used was all toddlers who came to the Simalingkar health center, amounting to 100 people. Data collection was carried out using interviews and analysis was carried out using bivariate and multivariate with multiple logistic regression. Results:The results showed that there was a significant influence between nutritional status, exclusive breastfeeding and parental smoking status with the incidence of ARI in infants. Conclusion:The results showed that there was a significant influence between nutritional status, exclusive breastfeeding and parental smoking status with the incidence of ARI in infants.