BACKGROUND Dental caries, traumatic dental injury (TDI) and malocclusion are common oral health conditions among preschool children and can have both physical and psychosocial consequences. Thus, it is important to measure the impact these on the oral health-related quality of life (OHRQoL) of children. The aim of the present study was to assess the impact of oral health conditions on the OHRQoL of preschool children and their families. METHODS A preschool-based, cross-sectional study was carried out with 843 preschool children in the city of Campina Grande, Brazil. Parents/caregivers answered the Brazilian Early Childhood Oral Health Impact Scale and a questionnaire addressing socio-demographic data as well as the parent's/caregiver's perceptions regarding their child's health. Clinical exams were performed by three researchers who had undergone a calibration process for the diagnosis of dental caries, TDI and malocclusion (K = 0.83-0.85). Hierarchical Poisson regression was employed to determine the strength of associations between oral health conditions and OHRQoL (α = 5%). The multivariate model was run on three levels obeying a hierarchical approach from distal to proximal determinants: 1) socio-demographic data; 2) perceptions of health; and 3) oral health conditions. RESULTS The prevalence of impact from oral health conditions on OHRQoL was 32.1% among the children and 26.2% among the families. The following variables were significantly associated with a impact on OHRQoL among the children: birth order of child (PR = 1.430; 95% CI: 1.045-1.958), parent's/caregiver's perception of child's oral health as poor (PR = 1.732; 95% CI: 1.399-2.145), cavitated lesions (PR = 2.596; 95% CI: 1.982-3.400) and TDI (PR = 1.413; 95% CI: 1.161-1.718). The following variables were significantly associated with a impact on OHRQoL among the families: parent's/caregiver's perception of child's oral health as poor (PR = 2.116; 95% CI: 1.624-2.757), cavitated lesions (PR = 2.809; 95% CI: 2.009-3.926) and type of TDI (PR = 2.448; 95% CI: 1.288-4.653). CONCLUSIONS Cavitated lesions and TDI exerted a impact on OHRQoL of the preschool children and their families. Parents'/caregivers' perception of their child's oral health as poor and the birth order of the child were predictors of a greater impact on OHRQoL.