Background.- Psoas abscess (PA) is a rare condition that presents diagnostic and therapeutic challenges and PA has been more frequently observed in recent years. The variable and nonspecific presentations of PA, as well as its infrequent incidence, can result in delayed diagnosis and misdiagnosis.Design.- Four cases diagnosed in our clinic are presented analyzing the main clinical features, microbiologic causal agents, risk factors and treatment.Results.- Four patients between the ages 17 and 67 years (mean: 45) were admitted to our clinic between October 1998 and December 1999. The mean delay to consultation was 30 days. The main symptoms were fever, lumbar pain. All patients were diagnosed by CAT. The casual microorganisms were: S. aureus, E. coli and Serratia marcescens. Three cases underwent open surgical drainage and death in one despite adequate medicosurgical treatment. One patient was exclusively treated with antibiotics.Conclusion.- PA is a serious health problem which presents with non-specific symptoms and signs. To reduce morbidity and mortality, it is important to diagnose the presence and extent of PA accurately using imaging studies. CAT is the method of choice for the diagnosis. The correct identification of the microorganisms, and the prompt use of the antibiotherapy associated to surgery, helped to a total recuperation of these patients. In some cases a multidisciplinary approach may be required.* Anahtar Kelimeler: Psoas, Apse* Key Words: Psoas, Abscess