This study, which is part of a Moscow longitudinal twin project, aims to explore genetic and environmental contributions to inter-individual variability of temperamental traits in adolescence on the basis of a Russian sample. 85 monozygotic (MZ) and 64 same-sex dizygotic (DZ) twin pairs aged 12 to 14 completed the children's version of the Rusalov Structure of Temperament Questionnaire (C-STQ). The results of model-fitting analyses indicate considerable hereditary determination of individual differences in 3 out of the 8 C-STQ dimensions - Social tempo, Object-related emotional sensitivity, and Social emotional sensitivity. Non-shared environmental effects explained the rest of the total variance in these dimensions. Individual differences in the remaining STQ dimensions were due to environmental factors.