BACKGROUND Retained products of conception (RPOC) is a rare complication following second-trimester delivery or pregnancy termination, often leading to significant hemorrhage. Diagnosed via ultrasound or CT, RPOC requires surgical intervention based on endometrial thickness. Risk factors include second-trimester abortion and use of placental forceps. We report a case of RPOC diagnosed 1 month postpartum after using a Bakri balloon for atonic hemorrhage during full-term delivery. CASE REPORT The patient, a 32-year-old woman with a history of 4 pregnancies and 3 births, conceived via frozen embryo transfer, which was her first infertility treatment. At 36 weeks of gestation, blood tests revealed a hemoglobin level of 10.4 g/dl. She delivered vaginally at 38 weeks 2 days, but postpartum uterine contractions were poor, leading to significant bleeding. Oxytocin administration and uterine massage failed to improve contractions, so a Bakri balloon was inserted. The total blood loss was 2263 cc, and 6 units of RBCs were transfused. The next day, the Bakri balloon was removed, and ultrasonography confirmed the absence of retained placenta before discharge on postpartum day 5. However, at her 1-month checkup, a retained placenta was diagnosed, requiring further intervention. The patient declined follow-up. CONCLUSIONS We encountered a case of RPOC 1 month after using a Bakri balloon. Although the relationship between the 2 remains unclear, it may be preferable to avoid such treatment in the future.