Urban solid waste (USW) is a public health problem worldwide that has not yet been completely evaluated in relation to childhood health. The main purpose of this study was to investigate associations between diarrhoea and exposure to USW among preschool children. A longitudinal study was carried out with 922 under-threes living in Salvador, Bahia, between 2000 and 2001. Both community and individual/home levels (strata) were evaluated by questionnaire and direct observation. The multilevel model, using Poisson regression with overdispersion, evaluated their contribution to the occurrence of diarrhoea. The children presented a mean longitudinal prevalence of 2.7% of days with diarrhoea during a mean period of 23 follow-up weeks. The main factors associated with diarrhoea were rubbish-in-street index [prevalence ratio (PR)=1.30; 95% CI 1.02-1.66] and intrahome rubbish packaging (PR=3.59; 95% CI 2.01-6.42). Other important variables were water-in-street index, child age, hygiene and cleanliness near the house, number of people per house, and drainage problems. The variables measured at the community level explained 4.77% of the variability of the children's number of days with diarrhoea.