Abstract: To determine the intensity of Pediculus capitis infestation (abundance) among school children, children`s sex and social factors were analyzed as modifiers of the general prevalence of parasitism. The study included 847 school children (407 girls, 440 boys) between 6 and 12 years, from 12 in public rural primary schools of Hamedan, Province of Hamedan, Iran. Classic prevalence was obtained as the percentage of children with nits and/or lice. The general prevalence was 6.85% (girls: 13.5%; boys: 0.7%, p< 0.001), head lice were much more commonly detected in girls than in boys. The obtained results showed that there was significant variations between head lice infestation and the factors such as parents` literacy, type of hair, previous infestation, sharing of bed and comb and care centers, while there was no significant variation between school grade, parents` job, members of family and pediculosis in the studied areas (p> 0.05). Sex and social factor are important modifiers of P. capitis general prevalence and degree of infestation. The classification of children by intensity of infestation allowed a more precise delimitation of this condition, which is especially important for disease surveillance and application of control measures.