Septic arthritis (SA) is a joint inflammation that develops secondary to infectious causes. SA in children is associated with a high rate of morbidity and mortality; therefore, it is regarded as an orthopedic emergency. Because SA of the hip joint usually mimics other musculoskeletal diseases, diagnosis remains challenging. Although this lesion usually shows a good outcome, treatment at an inappropriate time, neglect, or inadequate treatment could lead to poor outcomes. We report on the case of a healthy adolescent who complained of episodes of fever and chills, weight loss, pain in his left hip, and limping. After performing necessary workups, two differential diagnoses of tumor and SA were made. The results of Gram stain and culture of the synovial fluid after surgical excision showed Klebsiella pneumoniae and Enterobacter cloacae complex. To the best of our knowledge, this is the first report of SA due to co-infection with K. pneumoniae and E. cloacae in a healthy patient.