An increasing number of patients with parotid gland tumors have been observed in recent years. The relationship between the immune system and tumor formation is thoroughly investigated. However, newly discovered molecules offer a new insight into the pathophysiology of malignancies. It would be ideal to find an easily determinable biomarker of tumor existence, its malignant potential or a biomarker suggesting the probability of disease recurrence. Our study is the first to examine serum concentrations of IL-33 and its sST2 receptor in patients with various types of parotid gland tumors. Serum IL33, sST2, IL-4 and IL-10 concentrations were determined in patients with benign and malignant parotid gland tumors (pleomorphic adenoma, Warthin's tumor, myoepithelioma and acinic cell carcinoma). We observed for the first time that serum IL-33 level was significantly elevated in patients with various types of parotid gland tumors and sST2 levels were significantly higher in pleomorphic adenoma and acinic cell carcinoma patients compared to the controls. Our results demonstrate for the first time that serum IL-33 and its sST2 receptor may be important factors in the pathology of parotid gland tumors. Although our results are promising, further investigations are required to detect if serum concentrations of those molecules may be a biomarker in parotid gland tumors. Impact statement Parotid gland tumors seem to be an increasingly important medical challenge, mostly due to a noticeable increase in the incidence. It would be crucial to find an easily determinable biomarker of tumor existence, its recurrence or malignant potential. We observed for the first time that serum IL-33 level was significantly elevated in patients with various types of parotid gland tumors and its sST2 receptor levels were significantly higher in pleomorphic adenoma and acinic cell carcinoma patients compared to the controls. We believe that our study helps to understand the biology of the tumors and a potential role of a relatively newly identified cytokine IL-33 in the pathophysiology of the parotid gland tumors.