To determine the spectrum of infectious agents of postoperative endophthalmitis, the relationship with the time of onset of symptoms after surgery and the antibiotic susceptibilities of the aerobic bacterial isolates.A retrospective review of microbiological records from January 1995 to December 1998 yielded 173 isolates from intraocular specimen of 170 patients with culture-proven postoperative endophthalmitis. Antibiotic susceptibility of these isolates was determined for various ocular antibiotics using the Kirby-Bauer disk-diffusion test. Based on the time of onset of illness, clinical presentation was classified into acute, delayed and chronic.Among 170 cases, 71 (41.7%) were attributable to gram-negative, 64 (37.6%) to gram-positive bacteria, and 37 (21.8%) to fungi. Gram-negative bacteria included P. aeruginosa (29;17.1%), other Pseudomonas spp (15;8.8%), non-fermenters (18;10.6%) and others (10;5.8%). Among these, 40 of 72 (55.5%) were sensitive to gentamicin, 47 of 72 (65.2%) to cefotaxime, 47 of 69 (68.1%) to amikacin, 52 of 71 (73.2%) to ciprofloxacin, and 25 of 40 (62.5%) to ceftazidime. The gram-positive bacteria included S. epidermidis (22;12.9%), S. aureus (13;7.6%), P. acnes (10;5.9%), Enterococcus spp (4;2.3%), Streptococcus spp (7;4.1%) and others (8;4.8%). Among these, 41 of 53 (77.3%) were sensitive to gentamicin, 47 of 53 (88.6%) to cefotaxime, 46 of 52 (88.4%) to ciprofloxacin, 38 of 41 (92.6%) to cefazolin and 27 of 37 (72.9%) to ceftazidime. All gram-positive bacteria were sensitive to vancomycin.In this large series of postoperative endophthalmitis, gram-negative bacilli followed by fungi accounted for the largest number of cases. A high degree of resistance of gram-negative bacilli to gentamicin, cefotaxime, amikacin and ceftazidime was recorded.