The aim of the study was to explore prevalence, interrelations and accuracy of assessing psychopathology, intelligence, and executive functions (EF) in preschool children with ADHD (age 2.1-6.5 years).We prospectively investigated 115 preschool outpatient children (91 boys, 24 girls, aged 4.3±1.0 years) with the clinical diagnosis of ADHD. Assessment included clinical history, background, psychosocial problems (CBCL, C-TRF), ADHD (DISYPS external ratings), cognitive performance (WPPSI-III, K-ABC), and executive functions (BRIEF-P, NEPSY).We found a high frequency of dysexecutive problems in up to 64 % in the parental BRIEF-P assessments, up to 62 % in the BRIEF-P teachers' assessments, and 62 % in the NEPSY functional assessments. Parental and teachers' BRIEF-P scores were only correlated in one subscale, inhibition, and NEPSY and BRIEF-P were not correlated at all. It was found that 42.5 % of the children with noticeable findings had agreeing results in all three, and another 45 % in two tests.About 2/3 of the ADHD preschool children had detectable EF dysfunctions. In order to assess dysexecutive problems, multi-method testing is mandatory.