BACKGROUND: The World Health Organization (WHO) defines mental health as ‘a state of well-being in which every individual realizes own potential, can cope with the normal pressures of life, is able to work effectively, and can make a contribution to community’. OBJECTIVES: Mental Health Problems (MHP) is a great concern for all societies in terms of its burden and impact. This survey screened MHP and its impact in an Iranian urban population aged 6 – 12 years old, and explored its associated socio-familial factors. PATIENTS AND METHODS: The survey was conducted in the elementary schools of Semnan, using random cluster sampling. Collection and analysis of data was performed using the parent version of the ‘Strengths and Difficulties Questionnaire (SDQ)’ and survey commands of Stata-nine, taking into account cluster effect and population weights. Associations were assessed by fitting simple and multiple logistic regression models. P < 0.05 was considered significant. RESULTS: With regard to the SDQ total score, 19.3% (95% CI: 8.6, 30.1) scored above the normal threshold (9.6% abnormal, 9.7% borderline). The frequency of problems ranged between 16.1% (peer problems) and 8.4% (emotional symptoms), and in all subscales boys were affected more than girls. The impact score was abnormal in 68.4% of all children, and was greater in girls than in boys. 'A previously diagnosed mental health disorder' (OR = 11.11, 95% CI: 5.55, 25.00), 'male gender' (OR = 1.43, 95% CI: 1.10, 1.87 and 'less time spent with the child by father' (OR = 1.61, 95% CI: 1.20, 2.17) were significantly associated with an abnormal SDQ. CONCLUSIONS: The high rate of MHP in 6 - 12 year-old children and the lack of any significant correlation with their age, underpins the importance of early screening for MHP in schools, with particular focus on high risk groups.