Abscess of the iliopsoas muscle is a rare condition that requires a high degree of clinical suspicion for diagnosis. High mortality rates highlight the need for prompt recognition. We report the case of a 26-year-old man, with a history of intravenous drug use, who was referred from an outside facility with sacral fracture and gluteal abscess. Sacral trauma occurred 3 weeks before presentation, with progressive worsening of buttock pain. The patient was treated with irrigation and débridement of the gluteal abscess. Follow-up MRI revealed a communicating iliopsoas abscess that initially had been undiagnosed. After a prolonged hospital stay requiring additional irrigation and débridement procedures, the patient was discharged in a stable condition. Five-month follow-up has demonstrated no evidence of recurrence of infection. To our knowledge, this is the first reported case of Staphylococcus aureus gluteal abscess with pelvic extension into the iliopsoas secondary to sacral trauma and intravenous drug use.