The cytokinesis-block micronucleus (MN) assay on blood lymphocytes is one of the most important tests implemented in cytogenetics for the measurement of genotoxicity. For the purpose of biological dosing, it is crucial to know the spontaneous frequency of MN and its normal values in general population, especially in children, which are used for the population databases. In this study, MN levels were investigated in cytokinesis-blocked lymphocytes of 150 apparently healthy children aged 1 to 15. Our aim was to assess the variability of MN values according to age and sex. The mean MN frequency among boys was 3.69 +/- 1.747 parts per thousand and 4.12 +/- 1.867 parts per thousand in girls where there was no significant difference in relation to age and sex. However, when we separated age groups as 0-2 years, 3-5 years, 6-10 years, and 11-15 years, one-way ANOVA test showed significant association. Significance was obvious in the 0-2 years age group with the 3-5 years age group and 6-10 years age group. When we grouped our study population as 0-2 years and 3-15 years, the mean MN frequency among the 0-2 years age group was 2.85 +/- 1.599 parts per thousand and 4.07 +/- 1.867 parts per thousand in the 3-15 years age group which was also statistically significant. This difference may be attributed to age-related increase of close contact with environmental hazardous agents. In conclusion, normal values of MN obtained in this study will add valuable information in regard to update the current childhood population data and will act as a reference for further genotoxicity studies.