It has been suggested that the development of uterine leiomyomas is positively influenced by an immune system in a chronically inflammatory state and that a lower level of regulating T cell (Treg cells) would play a central role. Since it has been suggested that the W620 variant of protein tyrosine phosphatase non-receptor type 22 (PTPN22) decreases the number of Treg cells, we investigated a possible relationship between PTPN22 polymorphism and uterine leiomyomas.We studied 203 white women from Rome who were hospitalized for symptomatic leiomyomas requiring surgical intervention. These women were considered in a previous paper regarding the relationship between ACP1 and dimension of leiomyomas. As controls we studied 355 healthy women from the same population with comparable age and without clinical evidence of leiomyomas. All women gave written informed consent to participate to the study. Chi square test of independence and T-test for difference between means were performed by SPSS package.Considering the whole sample, a borderline association between PTPN22 and leiomyomas was observed: the *C/*T genotype is more frequent in cases than in controls. This association is marked and statistically significant in younger women only. The main diameter of tumor is significantly greater in *C/*T than in *C/*C women. This effect is present in younger women only. The *C/*T genotype also shows a higher tendency to intramural localization, but no effect of age is observed upon this association.The data suggest a positive effect of *C/*T genotype on susceptibility to leiomyomas in younger women. In these women a *C/*T genotype favors the growth of leiomyomas.