Type 1 diabetes mellitus is a chronic disease characterized by autoimmune degradation of insulin-producing beta-cells. It was shown in a number of epidemiological studies of seasonality of birth in children with type 1 diabetes that the autoimmune process began during fetal and postnatal development. No such studies were carried out in the former Soviet Union countries. The aim of the present study is to compare the seasonal birth month pattern in patients with type 1 diabetes (10780 men and 9337 women) born in 1960-2002 to that in the total population of Ukraine (14 785601 men and 13 911370 women) born during the same period. Significant differences were found between these two populations: chi-squared = 103.97, p < 0.0001 and 135.17, p < 0.0001 in men and women, respectively. The results of cosinor analysis showed similar sinusoidal birth patterns of patients with type 1 diabetes in all sub-groups, irrespective of the age of clinical disease expression: 0-9, 10-19, or 20-29 years. In all cases, the highest and lowest predispositions to type 1 diabetes were inherent in the people born in spring and autumn, respectively. We propose that seasonal differences in the birth pattern in the two above populations could be due to long-term programming of glucose-insulin metabolism determined by the effect of certain seasonal factors during early ontogenesis.