To translate into Castilian (Spanish) and measure the validity of the ECBI (Eyberg Child Behaviour Inventory), a questionnaire to screen behavioural disorders in pre-school children.Translation and back-translation of the ECBI. A descriptive crossover study.Primary Care Paediatrics.All the 3, 4 and 5-year olds from 4 paediatric clinics at 4 Health Centres (n = 527). One refusal.The questionnaire was filled in by the children's mothers and was repeated 20 days afterwards for 35 children. High coefficients of internal consistency (Cronbach's alpha = 0.87) and stability (intragroup correlation = 0.89 [0.78-0.94]) were obtained. There was good factorial validity, as 84% of the variance was explained by the four factors with value greater than 1.The Spanish version of the ECBI is a brief and easy questionnaire with good results in psychometric assessment. Therefore, it can be recommended for use in paediatric Primary Care in order to detect children with behavioural problems.