We studied the bacteriology of maxillary sinus aspirates obtained from patients diagnosed with chronic sinusitis. We recovered 659 strains from 510 aspirates; of these, 572 (86.8%) were aerobes and 87 (13.2%) were anaerobes. Aerobes only were recovered from 310 of the 510 specimens (60.8%) and anaerobes only from 31 (6.1%). Among the 572 aerobic bacteria, the most prevalent organisms were Streptococcus viridans (158 strains [27.6%]), Streptococcus pneumoniae (67 [11.7%]), Corynebacterium species (66 [11.5%]), Staphylococcus aureus (54 [9.4%]), Moraxella catarrhalis (38 [6.6%]), Hemophilus parainfluenzae (33 [5.8%]), and group C beta-hemolytic streptococci (26 [4.5%]). Among the 87 recovered anaerobes were species of Peptostreptococcus (32 strains [36.8%]), Prevotella (22 [25.3%]), Actinomyces (13 [14.9%]), Propionibacterium (11 [12.6%]), Fusobacterium (8 [9.2%]), and Veillonella (1 [1.1%]). Beta-lactamase production was detected in 115 of the 572 aerobic strains (20.1%) and in 10 of the 87 anaerobic strains (11.5%). We found that the prevalence and type of organisms we identified in chronic sinusitis did not differ substantially from those reported in previous studies. Our study is one of the more extensive reports on the type and prevalence of pathogens in chronic sinusitis that has been published to date.