Tuberculosis psoas muscle abscess is currently an uncommon clinical entity in industrialized countries. It was considered the predominant cause of these abscesses in the early part of the 20thcentury as a result of complicated Potts disease. We describe the case of a psoas abscess caused by the combination ofMycobacterium tuberculosisandStaphylococcus aureus. In this patient, the abscess was not associated with Potts disease but with osteomyelitis of the iliac crest, in which the evaluation with magnetic resonance imaging was very specific in determining the extent and regional spread.