e17559 Background: Olaparib (poly(ADP-ribose) polymerase inhibitor) is a relatively new anticancer drug and some of its metabolic side effects, such as its effect on blood glucose, are not yet well defined. The aim of the study was a retrospective analysis to investigate olaparib-induced changes in glucose levels in patients with ovarian cancer (OC). Methods: The study was conducted on 32 OC patients with normoglycemia (3.9–5.5 mmol/l) confirmed before olaparib treatment. The fasting glucose (FG) levels were estimated after I (one month), II (two months), and III (three months) courses of olaparib treatment. The severity of hyperglycemia was graded according to the Common Terminology Criteria for Adverse Events (CTCAE v5.0). Results: During treatment with olaparib, grade 1 hyperglycemia was found in 18 patients (56.2%), therefore hemoglobin A1C level measurement was recommended. The number of patients with impaired fasting glucose (5.6–6.9 mmol/l), characteristic of a pre-diabetic state, was 17 (53.1%), while glycemia indicative of diabetes (≥7.0 mmol/l) were found in 1 patient (3.1%). The statistically significant increase in glycemia was observed after I course of treatment (p< 0.0001), then after the second (p=0.0003), and III course (p=0.0025). Conclusions: During olaparib therapy, hyperglycemia was observed in 56.2% of the analyzed OC patients, implying the need for glycemic monitoring during monthly routine check-ups to implement effective behavioral and therapeutic management.