|Staphylococcus lugdunensis is a member of coagulase-negative staphylococci (CoNS) which is uncommon microbial culture isolate with virulent potency. Despite CoNS are usual skin commensals and often regarded as contaminant or colonizer when isolated from cultures of clinical specimens, clinical course and microbiological characteristics of Staphylococcus lugdunensis may resemble those of Staphylococcus aureus rather than other CoNS. Invasive infectious diseases such as infective endocarditis, peritonitis, skin and soft tissue infection, vascular prosthetic infection,septicemia, osteomyelitis have been described to be associated with Staphylococcus lugdunensis. We report the first case of psoas abscess caused by Staphylococcus lugdunensis in Korea. A 45-year old woman presented to a community hospital with fever and right flank pain. On admission date, her body temperature was 37.8℃, laboratory test revealed white blood cell count of 18950 cells/μl (90.7% neutrophils), ESR of 77 mm/hr, CRP of 22.86 mg/dl. Abdomen-pelvic CT scan was obtained, which illuminated 12x5cm sized right-sided psoas abscess. Percutaneous abscess drainage was performed and culture from the drained fluid isolated oxacillin-sensitive Staphylococcus lugdunensis. Initial antimicrobial therapy, intravenous ceftriaxone plus metronidazole, was maintained for 15 days. Defervescence and normalization of leukocytosis and CRP level was achieved, and the patient was placed on oral ciprofloxacin. After 9 days of administration of oral ciprofloxacin, patient was transferred to a tertiary teaching hospital due to prolonged treatment and for further management. Cefazolin was administrated intravenously. On 26th day of total antibiotics therapy, interval reduction of size of abscess was noted on CT. The patient was discharged for outpatient follow-up with oral ciprofloxacin and rifampicin in consideration of antibiotic sensitivity and tissue penetration. To our best knowledge, this is the very first case report of Staphylococcus lugdunensis psoas abscess in Korea.