We have studied 18 patients with abscess at the psoas who had a mean age of 43.55 +/- 18.9 years and a predominance of males (77.8%). In nine cases the abscess was secondary to a lumbar discal spondylitis, in 5 cases to a sacroiliitis, in one case to abdominal disorder, and 3 cases the abscess was considered of a primary origin. The etiologic agents were S. aureus (8 cases), E. granulosus (5 cases), M. tuberculosis (3 cases), and B. melitensis (1 case). In one patient the infective agent was not isolated and in two cases the abscesses were infected by E. granulosus and P. aeruginosa. The clinical picture on admission was studied in all cases. Microbiological and pathologic analysis of the abscess allowed to establish the diagnosis in 11 cases (yield: 84.6%). Computerized axial tomography was the most useful imaging technique. Antimicrobial treatment was undertaken in 16 cases. Four patients recovered with pharmacological treatment alone. Surgical treatment was performed in 13 cases. Aspirative punction/drainage was carried in only one patient. The clinical course was favourable in 16 patients (88.9%). Our data indicate that the incidence of abscess of the psoas in cases of intraabdominal infections is low. In our series the incidence of abscesses secondary to hydatidosis is relatively high.