This study assessed the prevalence and associated factors of pneumonia among children under-five years presenting with acute respiratory symptoms. This was a cross sectional study at the Pediatric Department of Kampala International University - Teaching Hospital, from the month of April to August 2019. The study included 336 children aged 2 to 59 months presenting with acute respiratory symptoms to the pediatric clinic. Pneumonia diagnosis was made according to the World Health Organization definition, modified by a chest radiograph. Structured questionnaires were used to collect data on socio-demographic, environmental and nutrition factors and multivariate logistic regression analysis using STATA version 13.0 was done to assess for the factors independently associated with pneumonia. Of the 336 children with acute respiratory symptoms, eighty-six, 86 (25.6%) had pneumonia. Factors significantly associated with pneumonia included: age below 6 months (OR=3.2, 95%CI=1.17-8.51, p=0.023), rural residence (OR=5.7, 95%CI=2.97-11.05, p <0.001), not up-to-date for age immunization status (OR=2.9, 95%CI=1.05-7.98, p=0.039), severe acute malnutrition (OR=10.8, 95%CI=2.01-58.41, p=0.006), lack of exclusive breastfeeding during the first six months (OR=2.9, 95%CI=1.53-5.53, p=0.001) and exposure to cigarette smoke (OR=3.0, 95%CI=1.35-6.80, p=0.007). The prevalence of pneumonia in children under-five years was high. Most of the factors associated with pneumonia are modifiable; addressing these factors could reduce this prevalence.