Spontaneous levels of the chromosome aberrations in the peripheral lymphocytes of 173 women were analyzed in the course of a medical examination of the residents of the Bryansk District territories (Klintsy Region, and the town of Klintsy) contaminated after the Chernobyl NPP accident in April 1986. The study population included only women who had been premenopausal at the time of the accident (mean age in 1986 was 23.9±0.7 years, ranging 2 to 56 years). The territory contamination with 137Cs ranged from 1.8 to 23.7 Ci/km2, the mean value being 7.5±0.2 Ci/km2. The range of the calculated absorbed thyroid doses was 30 to 340 mGy (in average, 52.3±3.3 mGy). The number of women with benign breast diseases (BBD) was 116 (67%). All recognizable chromosome lesion types were scored in the first in vitro division metaphases stained with azure-eosin. The mean total aberration frequency in the sample studied was 3.5±0.2 per 100 metaphases, the main contribution being made by the chromatid deletions, which is typical for a normal spontaneous aberration pattern. Based on the results of the cytogenetic analysis, the study population was subdivided into two groups. Group A (128 women) included subjects who showed normal patterns of spontaneous chromosome aberrations. Abnormal patterns, including the aberration frequencies significantly (at p<0.05) exceeding the mean group value and/or the presence of chromosome type exchange aberrations, were found in 45 women (group B). Statistical hypotheses on the possible correlations between the cytogenetic anomalies, BBD, level of the territory radiation contamination, and the absorbed thyroid dose were tested. The proportion of women with BBD was approximately the same in groups A and B (68 and 64%, respectively; p=0.665), which did not allow us to state that abnormal chromosome patterns can be used as diagnosis markers. The data obtained showed some positive trends between the cytogenetic anomalies, breast disorders, level of the territory contamination and the thyroid dose. In addition, it is interesting to note that the inclusion of the body mass index (BMI) into the data analysis showed that, both in women with cytogenetic anomalies (group B) and among the women with BBD, this index was essentially lower than in the respective comparison groups. The BMI differences could not be explained by the age differences, since the latter were insignificant in all the cases (p>0.8).