Objectives: We aimed to determine objectively the effect of the passive smoking on otitis media with effusion (OME) and recurrent otitis media (ROM) by using the method of cotinine urinalysis. Study Design: We designed a prospective case control study with follow-up of the case group for 1 year after insertion of tympanostomy tubes to evaluate postoperative complications such as otorrhea and early extrusion (<6 months), in case a significant risk factor was found. Methods: One hundred fourteen children between 3 and 8 years of age requiring tympanostomy tubes because of OME and ROM were chosen and compared with 40 age-matched children, Exposure to environmental tobacco smoke was assessed by cotinine urinalysis, which was performed by means of the radioimmunoassay method. Results: In this study, 73.7% (84 of 114) of the children in the case group and 55.0% (22 of 40) of the children in the control group were found to be "exposed" (P = .0461). This difference was statistically significant. Comparing the cotinine urinalysis results with parental smoking histories, 23.1% (9 of 39) of the children without parental smoking histories were "exposed" to tobacco smoke versus 84.3% (97 of 115) of the children with parental smoking histories (at least one person smoking). Conclusions: Our results indicate that sidestream smoking increases the risk of OME and ROM. Legal regulations and guidelines must be established to protect children from passive smoking. Because cotinine urinalysis is a noninvasive and reliable method for the determination of passive smoking, it can be used for that purpose.