Background: Interleukin-19, a member of the interleukin-10 family of cytokines,contributes to breast cancer pathogenesis. High interleukin-19 expression in breasttumor tissues is associated with poor clinical outcome. This study aimed to assessthe changes in serum level of interleukin-19 in breast cancer patients in comparisonwith normal women and its association with the clinicopathological parameters ofthis disease.Methods: Enzyme-linked immunosorbent assay was used to analyze serumlevels of interleukin-19 in 116 women with breast cancer before chemotherapy orradiotherapy, and in 60 healthy age-matched women without any acute or chronicdiseases or family history of cancer.Results: There were significantly lower serum interleukin-19 levels in breast cancerpatients (median: 27.3 pg/ml; range: 10.5-2443.6 pg/ml) compared to healthycontrols (median: 35.1 pg/ml; range: 10.9-13676.6 pg/ml; P<0.01). Compared to the healthy control group, the decrease in serum interleukin-19 concentration was seen in all breast cancer stages. However the decrease was only significant for stage III (P=0.02). We found no significant association between serum interleukin-19 levels and stage, grade, lymph node involvement or other clinicopathological variables of the disease. However, when compared to the healthy control group, we found significantly decreased serum interleukin-19 levels in patients with involved lymph nodes (P<0.01) or tumor size greater than 2 cm (P=0.01).Conclusion: There were significantly decreased interleukin-19 levels in breastcancer patients compared to the healthy control group. We observed no associationbetween serum interleukin-19 levels and clinicopathological parameters in breastcancer patients.