e16579 Background: CA 125 is known and useful marker in diagnosis and follow up of patients with ovarian cancer. But there is only a few study about YKL-40 and its usefulness in these patients. The aim of our study was to compare the serum levels of YKL-40 and CA 125 in patients with active phase of ovarian cancer disease (during diagnosis and recurrence). Methods: We analyzed 58 women with ovarian cancer hospitalized and treatment in period from January 2006 to March 2008. Group I - 42 patients constituted women with actually diagnosed ovarian cancer and group II women with recurrence of ovarian cancer. Results: Mean value of YKL-40 in patients with just diagnosed ovarian cancer was 181 ng/mL (16.42–766.1 ng/ml). Mean value of YKL-40 in patients with the recurrent of ovarian cancer was 122.38 ng/mL (9.47–389.22 ng/mL). CA 125 respectively 729.58 U/mL (10.62–4882.1 U/mL) and 579.15 /mL (5.38–6000 U/mL). When the cut-off level for YKL-40 was set at 130 ng/mL we found elevated serum levels in 50% of group I and 38% of group II. Respectively in group I we found 73% elevated values of YKL-40 and 44% in group II when the cut-off level was set at 61 ng/mL. In patients with diagnosed ovarian cancer percentage of elevated CA 125 serum value was 90% and 55% in recurrent ovarian cancer (cut-off level -35 U/mL). Conclusions: Significance of YKL-40 tumor marker in ovarian cancer diagnosis seems to be less then known CA 125 antigen. No significant financial relationships to disclose.