Environmental tobacco smoke (ETS) has been regarded as one of the most important public health issues. It has been estimated that approximately 75% of Turkish children are exposed to ETS. In this study the parental smoking habits were determined. Then, the relationship between parent-reported estimates of children's exposure to ETS in the home and children's urinary cotinine levels was examined. According to the reports of parents, 57.8% of the fathers and 23.3% of the mothers were current smokers, 69.8% of the children came from homes with smokers, and 53.4% had daily exposure to ETS. Urinary cotinine levels were significantly higher in the exposed group than the nonexposed group. This data showed that ETS exposure was prevalent and a combination of a parent-report and a biological measures is suggested as the most informative estimate of ETS exposure in children.