Aim:The goal of this study was to evaluate the impact of passive smoking on the development of lower respiratory tract infection (LRTI) in children aged 0-24 months. Material and Method:95 infants with LRTI and 95 healthy control infants were included in the case-control study conducted by random sample method. Urinary cotinine/creatinine ratios (u-CCR) were determined in all children. Smoking habits of their parents were evaluated. Data were analysed by Chi-square, Mann-Whitney U and Pearson correlation tests. Results:The frequency of LRTI was increased in children with exposure to passive smoking. The incidence of LRTI was also increased as the number of cigarettes smoked increased. The infants whose mothers were active smokers had more LRTI compared to those whose mothers were non-smokers (OR= 2.5, p= 0.026). The prevalence of passive smoking was quite high in both group sof children according to u-CCR (95.8%, 92.7% respectively). The prevalence of passive smoking detected with quantitative measurements among children was higher than parental self reports. Conclusions:Passive smoking prevalence was very high in infants with LRTI and in healthy infants. However, passive smoking exposure and smoking density among infants with LRTI were higher than healthy infants.