The Behaviour Rating Inventory of Executive Function--Preschool Version (BRIEF-P) is a hand-storable instrument that permits evaluation of the executive functions in children between the ages of 2 years and 5 years 11 months by parents, teachers, or other usual child caregivers, thus facilitating early intervention. It is a standardized questionnaire that is derived from the school version. It has been translated into different languages and adapted to different cultures and recently it has been translated into Spanish. It is answered using a Likert-type frequency scale. It is composed of 63 items that measure various aspects of executive functioning: five clinical scales, three broad indexes, one composite score or Global Executive Composite, and validity scales. The objective of this study was to analyze the psychometric properties related to the validity and reliability of BRIEF-P in children with neuropsychological, psychological, and developmental disorders that begin to manifest during early years. Non-experimental or ex post facto research was the method used. The participants were 107 parents and 98 teachers, evaluating 205 children. We analyzed several psychometric properties, related to reliability and validity, and compared the results with normative and clinical samples in the versions (parents and teachers). It is confirmed that BRIEF-P is a valid and reliable instrument with which to evaluate executive functions in children having neurodevelopmental disorders. We believe that BRIEF-P can be an especially useful and advisable instrument to be applied by educational psychologists and children's clinicians in a population. BRIEF-P is discriminative and sensitive to executive deficits in the clinical population.