The average incidence rates of type 1 diabetes in Lithuania were lower among females than among males in 20-24, 25-29, and 30-34-year-aged groups. A clear male predominance of type 1 diabetes was seen in all ages during 1983-2002 in Sweden. The average incidence rate of type 1 diabetes was 12.7 per 100,000 person years (16.4 and 8.9 among males and females) [
15]. The male predominance in the majority of 24 populations and the female excess in 9 of them were well discussed by Östman et al. in 2007 [
15]. The male excess was not related to the high, intermediate or low level of the incidence [
15]. In Lithuania, the average incidence rates of 1983-2007 year of type 1 diabetes in 0-4-year-aged group among boys and girls did not differ significantly, in 5-9-year-aged group the incidence of type 1 diabetes was significantly higher among girls than among boys. The disappearance of gender difference starts during the puberty in 10-14-year-aged group [
28]. The results of the present study showed that significant male predominance of the incidence rates of type 1 diabetes started in 20-24-year-aged group, and increased with the age of the onset of disease. The highest gender difference with male predominance was observed in 30-34-year-aged group in Lithuania. We did not find any possible cause of under-reported cases among females in 15-34-year-aged group. Environmental exposures may differ for females and males. The results of Swedish study suggest that gestational enterovirus infections may be related to the risk of the offspring developing type 1 diabetes in adolescence and young adulthood. Boys of enterovirus IgM-positive mothers had approximately 5 times greater risk of developing diabetes, as compared to boys of IgM-negative mothers [
38]. There are innate differences in the function of the female and male immune systems, and there is some evidence for differences between females and males in the ability of a target organ for autoimmunity to withstand damage [
39]. Besides a genetic basis, sex hormones affect the function of the mammalian immune system and make undeniable contributions to the sexually dimorphic expression of autoimmune disease [
40]. Sex hormones seem to be secondary players that are responsible for helping in a process that may have been triggered by others. Androgen promotes autoimmune diseases with a profile of type 1 cytokines [
41]. The poor induction of factors that mediate down-modulation of T-cell responses upon stimulation in type 1 cytokine environment may contribute to the development of autoreactive type 1 responses in the target tissue of type 1 diabetes [
42]. Indeed, it suggests that males are more susceptible to environmental agents. Male excess has previously been reported and was largely restricted to those patients carrying the HLA-DR3/nonDR4 genotype [
43]. Results of another study do not support a significant involvement of the Y chromosome in DR3/nonDR4 type 1 diabetic cases in early-onset type 1 diabetes as a whole [
44]. Other explanations, such as X chromosome-linked inheritance, are thus required for the male bias in incidence in type 1 diabetes in Sardinia [
44].