STUDY DESIGN: This is a retrospective study on the clinical availability, diagnosis and treatment of primary psoas muscle abscess. OBJECTIVES: This study investigated the causes and clinical results of patients with primary psoas muscle abscess. SUMMARY OF LITERATURE REVIEW: Primary psoas muscle abscess is not a common disease clinically, but it is a very dangerous disease if the diagnosis and treatment are delayed. MATERIALS AND METHODS: Between October 2003 and February 2010, we investigated the symptoms, pathogens, the associated diseases and treatments of 17 patients (11 males and 6 females; mean age: 49.5 years old). We divided patients into the 3 groups According to the treatment options (Group 1: antibiotics alone, Group 2: percutaneous catheter drainage, Group 3: open drainage) and the correlation of the abscess size of each group was analyzed by the Kruskall Wallis method. RESULTS: The most common complaint was lower back pain (14 patients). Staphylococcus aureus was the most common infectious organism (12 patients). All the patients were treated with broad spectrum antibiotics. Group 1 was composed of 4 patients and the average size of the abscess was 2.3cm (range: 1.2~4.5cm). Group 2 was composed of 7 patients and the average size of the abscess was 7.4cm (range: 3.8~12.2cm). Group 3 was composed of 6 patients and the average size of the abscess was 8.1cm (range: 6.1~14.7cm). There was a significant correlation of the abscess size between each group. (p=0.0007) CONCLUSIONS: The patients diagnosed with primary psoas muscle abscess complained about lower back pain, a febrile sense and gastrointestinal symptoms. Most of the primary psoas muscle abscesses are pyogenic infections. We have to use broad-spectrum antibiotics for the initial treatment. When the occasion demands, additional treatment like percutaneous catheter drainage and open drainage should be considered.