The prevalence of extended-spectrum beta-lactamases producing Enterobacteriaceae (ESBLPE) among nosocomial and community acquired isolates was studied (September, 1999 - August, 2000). Nosocomial and OPD isolates (200 each) were collected from OPD and different wards of the Pakistan Institute of Medical Sciences (PIMS) Islamabad, Pakistan, and tested for the production of ESBLs using the double disc diffusion technique. The prevalence of ESBL was highest in nosocomial isolates among the patients of age group III (50-60 years) (48%) with Escherichia coli as the most prevalent organism. ESBL positive isolates were mostly reported in males (65.33%) compared to females (34.67%).