Considering hospitalization as an indicator of seriousness of acute respiratory infection (ARI), this study focuses on the association between some environmental factors with the need for hospitalization of children with a diagnosis of ARI. The study analyzed all the medical records (at the Municipal Emergency Ward in Cuiabá, Mato Grosso State) of children under five years of age (both sexes), collected by month of attendance. Two weather seasons were considered: dry (May-October) and rainy (November-April). Variables included: temperature, relative humidity, and number of fires (due to extensive slashing and burning for agriculture in the region). Prevalence of ARI was 49.8%, and hospitalization was required in 7.6% of cases, with a higher percentage during the dry season. The dry season and lower relative humidity were associated with increased pediatric hospitalization rate due to ARI.