Iliopsoas abscess (IPA) is uncommon in childhood and very rare in the neonate and infant. We present a case of IPA after an umbilical granuloma in an infant. A baby girl with a birth weight of 2,970 g was born at thirty-seven weeks and two days gestation by Caesarean Section. On the fourteenth day after birth, her umbilicus was wet and developed the granulomatous formation. At two months of age, she presented with right leg and groin swelling with mild bluish discoloration and without fever. She had poor movement of her right leg and showed apparent discomfort. Her umbilicus was dry and there was no granulomatous material. Ultrasonography and computed tomography demonstrated an iliopsoas abscess in the right position. Therefore, an extraperitoneal surgical drainage was performed, aspirating yellowish pus. Culture of the purulent material revealed Staphylococcus aureus. Systemic antibiotic therapy was continued for ten days. After three days of drainage, full-range motion of the right leg was gained, and then after eleven days, CT findings comfirmed the disappearance of the iliopsoas abscess. IPA is extremely rare and it is difficult to diagnose. However, it should be included in the differential diagnosis of an infant with poor leg movement and swelling of the groin to the femur.