[Septic sacroiliitis with a horseshoe-shaped abscess diagnosed by MR scanning]

One case of septic sacroiliitis with a horseshoe-shaped abscess is presented. Due to magnetic resonance imaging (MRI) treatment was started the day after arrival to the hospital. Despite relevant antibiotic treatment the abscess did not resolve and after three weeks surgery with drainage was performed with good result. After half a year there was only a slight discomfort. The role of MRI is emphasized.