The study of cytogenetic abnormalities may lead to a more accurate localization of genes related to disease. Therefore, chromosome determination could be included among the routine investigations of patients with bipolar disorder. We have examined the chromosomes of 80 patients with bipolar disorder and 30 controls by using the GTG banding technique. Random numerical and structural variations were present in 26.3% of the patients and in 10% of the controls. Of these, 57.1% and 42.9% of abnormalities had structural and numerical aberrations, respectively. Structural aberrations usually consisted of deletions, heterochromatic regions of chromosome 9, and partial trisomy of various chromosomes. Numerical chromosome anomalies were present in 9 cases (42.9%), and included trisomy 21, monosomy X, 47,XXY, marker, and acentric chromosomes. The frequency of sex chromosome changes in our populations (3.75%) was significantly increased compared to that in newborns. These regions can be the most active hotspots in the genomes of bipolar patients. The identification of such chromosomal abnormalities associated with bipolar disorder could provide important implications for further research to locate disease-related gene(s) on the chromosome(s).