The goal of the study was to find ways to improve the quality of preoperative diagnosis of mucinous cystic liver neoplasms using such tumor markers as CA 19-9 and telomerase activity. We conducted a retrospective analysis and a prospective study that included the results of treatment of 80 patients with cystic neoplasm of the liver (31 with MCNL, 36 with multichamber non-parasitic cysts (NPC), 13 with stage II (WHO classification) echinococcus liver cysts. Our study showed the presence of telomerase activity in 29 (93.5%) patents with MCNL (in case of IMCNL, the TA was high both in the tumor itself and the CNL content).16 patients demonstrated high TA (+++) both in the tumor itself and the CNL content; 11 and 2 patients had moderate (++) and low (+) TA, respectively. 12 (38.7%) patients with MCNL had the CA 19-9 level above 1000 U/L, 14 (45.1%) - above 10,000 U/L, and 3 (9.6%) - above 100,000 U/L, while only 1 (6.5%) patient had the CA 19-9 level <1000 U/L. The analysis of data showed the absence of TA in the CNL content in 33 of 36 patients with NPC. However, three patients demonstrated a low activity of telomerase. CA 19-9 levels were below 1000 U/L in 27 (75%) of 36 patients with NPC. It was established that the determination of TA and the level CA 19-9 in the contents of the CNL is a valuable method, which makes it possible to carry out a preoperative differential diagnosis of CNL with a high probability.