Recent reports describe the emergence of antimicrobial resistant bacteria in acute sinusitis and an increased incidence of enteric gram negative bacilli in chronic sinusitis. The objective of this cross sectional study is to identify the emergent resistance patterns in bacterial chronic sinusitis. Specifically, this article seeks to characterize the bacteriology of outpatient chronic sinusitis, then to compare the antimicrobial susceptibilities of the bacterial isolates with standard culture data from a tertiary care center. Between March and August, 1994, 113 new outpatients presented with chronic sinusitis at a major teaching institution. Of these patients 34 underwent endoscopically guided aerobic culture of the paranasal sinuses and nasal cavities. Of the 48 total cultures, there were 43 positive cultures yielding 72 isolates. Thirty-eight cultures had two or fewer isolates; four cultures had three plus isolates, and one culture grew out normal flora. The most frequently isolated organisms were coagulase negative Staphylococcus (SCN), 20 (28%); Pseudomonas aeruginosa, 12 (17%); and Staphylococcus aureus, 9 (13%). Within the limited sample size for each isolate, Staphylococcus coagulase negative, Pseudomonas, and Pneumococcus demonstrated higher antimicrobial resistance compared to the medical center's corresponding nonurinary isolates. Additionally, three of six patients with Pseudomonal aeruginosa (50%) had a quinolone resistant strain. These preliminary data suggest that both an increased incidence of antimicrobial resistance and of enteric gram negative bacilli may exist in these outpatient, tertiary care center patients with chronic bacterial sinusitis.