A case of unilateral psoas abscess in a 58-year-old patient, shortly after posterior lower spine stabilization and fusion for spinal stenosis using transpedicular spine fixation is reported. The diagnosis was delayed because the patient's symptoms were referred to the thigh and the plain roentgenograms were negative for pathology. The technetium scintigram and computed tomography (CT) helped localization, diagnosis and treatment of the psoas abscess. Percutaneous CT-guided drainage was followed by recurrence of the abscess, and open surgical evacuation was performed successfully in combination with antibiotic treatment for 8 weeks. Psoas abscess should always be suspected when recurrent pain is associated with fever and elevated erythrocyte sedimentation rate after instrumentation of the lumbar spine. Hardware of a low profile and volume should be used to decrease dead space in the fusion area, and the volume of bone substitutes should be limited for the same reason.