We studied hyperactivity syndrome and attention and concentration deficit in preschool children of kindergartens of Tehran. In this relation, etiological factors causing this behavioral disturbance have been also taken into consideration. This is a descriptive, analytic, cross-sectional study including 400 children together with their parents and teachers, performed in 2001. 4 samples from every kindergarten were selected randomly. The incidence of hyperactivity and attention and concentration deficit was estimated to be 11%, of which 60% were male. 79% were first-born children to their parents. Hyperactivity and deficit of attention and concentration were positively related to the marital position of the parents (Divorced parents), occupational absence of parents from home more than 8 hours per day, illiteracy or low education and a history of psychiatric illness of the mother.