Aim of this study was to determine the probability of occurrence of Attention Deficit/Hyperactivity Disorder- ADHD in children of preschool age and early school age, and to identify differences in the assessment of children identified with high probability for the disorder with regard to assessment by parents and teachers, and with respect on age and sex of children. Total of 107 children were included in the study: 51 girls and 56 boys. The study employed two questionnaires: Questionnaire for Analysis at School for teachers and Questionnaire for Analysis at Home for parents. Both questionnaires contained 39 statements which covered three dimensions of child's behavior needed for ADHD diagnosis. Raw data in each questionnaire were converted according to the standard norms of Guide to Standard Scores (SS) and Total Standard Scores (TSS) and as such were used for statistical analysis. It was found that a considerable number of children demonstrated high probability for ADHD disorder in assessments done by both parents and teachers. Parents recognize probability of ADHD presence more frequently among male children, while teachers recognize this probability more often among female children. Research shows that a significant percentage of children from the entire sample have been labeled with significant ADHD symptoms. Given the age of the child both parents and teachers recognize similar levels of high ADHD probability. Future studies should be directed toward early detection and recognition of children with ADHD syndrome, and clinical evaluation as a first step toward successful treatment and prevention of additional psychological and other problems in an adult.