The family, where 2 children had partial trisomy 2q33-q ter, due to paternal translocation t(2;18) (q33;p11.1), was examined. The analysis of 36 cases of trisomy 2q showed that the forms connected with parental chromosomal rearrangement prevailed in the genesis of trisomy 2q. Moreover, the balanced carrier-mothers were more common than fathers. The 2q34-q ter segment may be considered "critical" for occurrence of trisomy 2q syndrome. In case of equal triplication, the similarity between the patients within the same family is greater than between those from different families. The value of intragroup similarity between the patients with equal trisomies may be used for evaluation of phenotypical similarity at different triplicated segments.