The study examined psychological development in 250 children at the age of 6-7 and 10-12 years who had been exposed in the prenatal period at the time of the Chernobyl accident in 1986. These children were compared to a control group of 250 children of the same age from non- and slightly contaminated areas of Belarus. The examination included psychiatric examination and intellectual assessment as well as the estimation of thyroid exposure in utero. The mean value of thyroid doses from ¹³¹I 0.39 Gy was estimated for the prenatal exposed children. The children of the exposed group had a lower mean full-scale IQ compared to the control group (89.6 ± 10.2 vs 92.1 ± 10.5 at the age of 6-7 years, P = 0.007; and 94.3 ± 10.4 vs 95.8 ± 10.9 at the age of 10-12 years, P = 0.117). Average IQ for the subgroup of highly exposed children (thyroid doses more than 1 Gy) was lower in comparison with average IQ for the whole exposed group (85.7 ± 6.4 vs 89.6 ± 10.2 at the age of 6-7 years, P = 0.014; 89.1 ± 7.1 vs 94.3 ± 10.4 at age 10-12 years, P = 0.003). No statistically significant distinctions in average IQ were found between the different subgroups of children in relation to the gestational age at the time of the Chernobyl accident. We notice a positive moderate correlation between IQ of children and the educational level of their parents (in exposed group - mothers: r = 0.50, P < 0.01 and fathers: r = 0.52, P < 0.01; in control group - mothers: r = 0.41, P < 0.05 and fathers: r = 0.42, P < 0.05). There was a moderate correlation between high personal anxiety in parents and emotional disorders in children (for mothers r = 0.38, P < 0.05; for fathers r = 0.43, P < 0.01). The relative risk of mental and behavioural disorders has been estimated for emotional disorders OR = 2.67, P < 0.001. The frequency of the formation of mental retardation, hyperkinetic disorders and other mental and behavioural disorders in children from both groups was approximately the same. We conclude that in the genesis of borderline intellectual functioning and emotional disorders in the exposed group of children a significant role was probably played by unfavourable social-psychological and sociocultural factors such as a low educational level of the parents, the break of microsocial contacts and difficulties adapting, which appeared following the evacuation and relocation from the contaminated areas.