BACKGROUND Previously we reported that airborne concentrations of cis-permethrin, but not trans-permethrin, measured during pregnancy in an inner city pediatric cohort was associated with cough by age 5. However, the effect of subsequent exposures to both permethrins during early childhood, and to piperonyl butoxide (PBO, a synergist for residential pyrethroid insecticides) remains to be elucidated. We hypothesized that prenatal and age 5-6 year measures of PBO and permethrins would be associated with cough at age 5-6 years in this cohort. Further, we explored the associations between these pesticide measures and wheeze, asthma, seroatopy, and fractional exhaled nitric oxide (FeNO). METHODS PBO and permethrins were measured in personal air during the third trimester of pregnancy and indoor residential air at age 5-6 years (n=224). Health outcome questionnaires were administered to the mothers of 5-6 year old children. Indoor allergen specific and total immunoglobulin (Ig) E production was measured from sera collected at age 5, and FeNO was measured at 5-6 years. The hypotheses were tested using regression models adjusting for common confounders. RESULTS Noninfectious cough was reported among 14% of children at age 5-6 years. Measures of prenatal PBO, but not age 5-6 year PBO or permethrins, increased the odds of cough [OR (95% CI): 1.27 (1.09-1.48), p<0.01; n=217]. No significant associations were found for other measured health outcomes. CONCLUSIONS Prenatal PBO exposure was associated with childhood cough. It is unclear whether the observed effect is due mainly to PBO itself or residential pyrethroids of which PBO is an indicator.