Increased levels of pollutants in the room, apart from the penetration of outdoor pollutants, can also come from indoor pollutant sources such as cigarette smoke, smoke from using firewood, and the use of mosquito coils. Pneumonia is the ultimate overlooked child killer (major “forgotten killer of children”). In Klaten District, pneumonia cases in the last 3 years have increased, 1,068, 1,244, and 1,705. This study was to determine the relationship between the incidence of pneumonia and exposure to smoke at home in children under 5 years of age in Klaten Regency, Central Java Province. This type of research is observational analytic with case-control studies. The total sample of 278 (139 cases and 139 controls) children under 5 years of age resided in Klaten Regency and were recorded as pneumonia cases in the public health care register in 2012 that met the inclusion and exclusion criteria. The research instrument consisted of a structured questionnaire. The results of data analysis showed that the relationship with the incidence of pneumonia in children under five was the variable exposure to cigarette smoke (OR= 2,053; p= 0,017 and 95% CI= 1,137-3,705) and exposure to kitchen smoke (OR= 2,664; p= 0,003 and 95% CI= 1, 4002-5, 0680). Factors associated with the incidence of pneumonia in children under 5 years of age in Klaten Regency, Central Java Province are exposure to cigarette smoke and exposure to kitchen smoke.