Objectives: This study was designed to examine the prevalence of depression among primary school children in Mashhad. Method: For this study 2071 four and five grade (10-12 years old) children (1049 boys, 1022 girls) were selected through random cluster sampling from all the seven educational districts in Mashhad; they were assessed in 1999–2000 using the Children Depression Inventory (CDI). The data were analyzed and further interpreted through application of non- parametric tests and statistical methods, Kolmogorov- Smirnov, Mann-Whitney, Wilcoxon and Kruskal-Walis, and linear correlation coefficients. Findings: The study demonstrated that the frequency of depression with a cut off point 20 in this city was 10.3%; depression was more prevalent among girls than boys (girls 13.1%, boys 7.6%). Moreover, the following variables were shown to effect childhood depression: divorce, changing neighborhood, changing school, family’s socio-economic status, number of family members, traces of neuropsychiatric disorders in the family, and death of relatives. Results: The results indicate that children must be considered as a target group in future prevention plans. Moreover, utilizing screening tests to identify depression in children will help the health authorities to take secondary preventive measures more effectively.