Analysis of <i>ESR1</i> gene haplotypes in relation to the rs2234693 and rs9340799 polymorphisms showed that the occurrence of TCAG and CCGG systems may be associated with a significant increase in the risk of ovarian cancer (OR 1.98, <i>p</i> = 0.043 and OR 2.45, <i>p</i> = 0.041, respectively). The gene discussed is ESR1; the disease is ovarian cancer.