Staphylococcus aureus is the commonest organism resulting in primary psoas abscesses. However, nonstaphylococcal
primary psoas abscesses have increasingly been published in the literature. Here, the author reports a case
of primary psoas abscess in a type II diabetic woman previously diagnosed Streptococcus agalactiae septicemia of unknown
origin, which rapidly responded to penicillin plus clindamycin and prompt surgical drainage. Diabetic patients are not only
susceptible to soft tissue infection but also primary psoas abscess caused by Streptococcus agalactiae.

Keywords: Primary psoas abscess, Streptococcus agalactiae, Group B Streptococcus