Purpose: The goal is to examine the prevalence, comorbidity and impairment of DSM-IV disorders in 3-year-old children from the Spanish general population. Method: A sample of 1,341 3-year-old preschoolers were randomly selected and screened for a double-phase design. In total, 622 families were assessed with a diagnostic semi-structured interview and functional impairment measures. Results: Prevalence of any diagnosis was 29.9 %, the most prevalent disorders being primary insomnia (11.7 %) and oppositional defiant disorder (ODD) (6.9 %). There were no sex differences in the prevalence. One-third of the families had sought professional help for the child’s symptoms, and 9.4 % received treatment (4.4 % psychological and 2.1 % pharmacological). After controlling for other comorbidities, ADHD was significantly associated with ODD, CD, insomnia and social phobia; ODD was associated with CD, separation anxiety, specific phobia and major depression. Diagnostic categories were associated with impairment, family burden, seeking professional help and receiving treatment. A diagnosis was more frequent in children of low socioeconomic status, born outside Spain, from one-parent families, with younger parents and with parents of lower educational level. Conclusions: Psychopathology, comorbidity and associated factors are very frequent from age three, suggesting a need for efforts of detection, prevention and treatment in the different societies.