Every loin swelling in an infant is not a renal mass: rare presentation of psoas abscess in an infant.

Primary iliopsoas abscess (IPA) in infants is an uncommon condition. It presents as inguinal or thigh swelling with limitation of movements on the affected side. Early detection and timely drainage of the abscess can prevent serious complications related to the dissemination of infection. We report a case of primary IPA due to methicillin-sensitive staphylococcal infection presenting as a left lumbar mass in an immune-competent infant. The abscess was detected in time, drained surgically and treated with cloxacillin for 4 weeks, thereby preventing serious complications.