To compare the bacterial aetiology and their in vitroantibacterial susceptibilities of acute and chronic dacryocystitis.A retrospective analysis of patients with clinically diagnosed acute and chronic dacryocystitis who underwent microbiological evaluation presenting between January 2000 and December 2005 was carried out. Mucopurulent discharge through punctum, pus from burst abscess, incision drainage, and lacrimal sac content were taken and subjected to microbiological evaluation.A total of 1891 patients of dacryocystitis were evaluated and subjected to microbiological evaluation, of which 566 (29.9%) had acute dacryocystitis and 1325 (70.1%) had chronic dacryocystitis. Of 1891 eyes, 1518 (80.3%) had pure bacterial growth and the remaining 373 (19.7%) had no growth. The percentage of culture-positivity was found to be higher in chronic dacryocystitis (90%) than in acute dacryocystitis (57.4%) (P<0.0001). A total of 1612 bacterial isolates were recovered from 325 acute and 1193 chronic dacryocystitis; in 1424 (93.8%) eyes, single bacterial species was isolated, and in the remaining 94 (6.2%) eyes, two bacterial species were isolated. The predominant bacterial pathogen isolated from acute dacryocystitis was Staphylococcus aureus(22.3%) followed by Pseudomonas aeruginosa(21.1%) and from chronic dacryocystitis was coagulase-negative staphylococci (CoNS) (44.2%), S. aureus(10.8%), and Streptococcus pneumoniae(10%). The highest percentage of bacterial isolates were susceptible to gatifloxacin (96.5%), ofloxacin (94.8%), and amikacin (91.1%). The percentage of resistance of bacterial isolates recovered from chronic dacryocystitis to gentamicin (45.7%), tobramycin (50.8%), norfloxacin (50.7%), and ciprofloxacin (30.4%) were found to be higher than that of bacterial isolates from acute infection to gentamicin (24.6%), tobramycin (35%), norfloxacin (36.5%), and ciprofloxacin (19.9%).The proportions of S. aureusand Pseudomonasspp are higher in causing acute dacryocystitis, while the proportion of CoNS is higher in chronic dacryocystitis. The percentages of antibacterial resistant isolates were higher among bacterial species from chronic dacryocystitis.