Despite in vivo studies suggesting that obesity increases carboplatin (CBDCA) bone marrow toxicity, the American Society of Clinical Oncology recommends that full weight-based cytotoxic chemotherapy doses be used to treat obese patients with cancer. Accordingly, the present study retrospectively investigated the effect of body mass index (BMI) on bone marrow toxicity in patients with gynecological cancer who underwent paclitaxel and carboplatin (TC) therapy after eliminating the effect of the target area under the curve (AUC). Risk factors for CBDCA bone marrow toxicity were also identified. A total of 110 patients with primary gynecological cancer or gynecological cancer of unknown primary origin who underwent TC therapy with a target AUC of 5-6 were included herein. Patients with a BMI of ≥25 and <25 kg/m2 were assigned to the obesity and control groups, respectively, and evaluated according to changes in hematological test values (platelet, white blood cell, and hemoglobin counts) starting from initial TC therapy administration until 21 d after the second treatment course. The obesity group had a significantly higher thrombocytopenia rate than the control group. Risk factors for thrombocytopenia ≥ grade 2 included BMI ≥25 kg/m2. Among patients with primary gynecological cancer or gynecological cancer of unknown primary origin who had a BMI of ≥25 kg/m2, those receiving CBDCA may be at increased risk for thrombocytopenia ≥ grade 2 when the dosage is calculated using the Calvert formula with the creatinine clearance level.