Data on interleukin-31 (IL-31) involvement in the patho-genesis of mastocytosis, and its impact on pruritus development in the disease, are limited. The aim of this study was to analyse distinct IL-31 gene polymorphisms in 127 patients (age 0.5-76 years) with mastocytosis and their correlation with clinical presentation, pruritus and serum IL-31 levels. In patients with mastocytosis, the frequency of IL-31 IVS2+12AA genotype and IVS2+12A allele was higher than in control subjects and they were linked to an increased risk of development of mastocytosis. In adult patients, but not in children, -2057AA genotype was also associated with an increased risk of occurrence of mastocytosis. Pruritus affected 83.3% of 78 adult patients with mastocytosis, and a positive correlation between serum IL-31 levels and pruritus was found in these patients. In conclusion, distinct polymorphic variants of the IL-31 gene may be involved in the pathogenesis of mastocytosis, and IL-31 may be involved in the induction of pruritus in patients with mastocytosis.