The authors investigated whether organochlorine exposure is associated with prevalence of otitis media, pneumonia, pertussis, asthma, and increased immunoglobulin E levels in children. Organochlorine concentrations and histories of infection and atopic manifestation were available for 343 children, and immunoglobulin E levels were available for 340 children. The authors applied logistic and linear regressions and controlled for confounders. In general, the prevalence of infections in children was not related to organochlorine exposure. However, for the combined effect of dichlorodiphenyldichloroethene with polychlorinated biphenyls or hexachlorobenzene, a significantly increased relative risk (odds ratios = 3.70 and 2.38, respectively) was found for otitis media. Exposure to dichlorodiphenyldichloroethene resulted in a significantly higher odds ratio for asthma (odds ratio = 3.71; 95% confidence interval = 1.10, 12.56) and in immunoglobulin E concentrations above 200 kU/l (odds ratio = 2.28; 95% confidence interval = 1.20, 4.31). This is the first study in which dichlorodiphenyldichloroethene has been identified as a substantial risk factor for asthma and for increased immunoglobulin E blood levels.