Sinus puncture and aspiration is an invasive procedure that hinders patient enrollment in studies of acute bacterial maxillary sinusitis (ABMS). Pain and minor bleeding also limit its potential diagnostic utility in clinical practice. Cultures obtained by rigid nasal endoscopy were compared with those from sinus puncture and aspiration in 53 patients with ABMS; 46 patients were assessable. Considering recovery of Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae from puncture and aspiration as the gold standard, endoscopy cultures demonstrated a sensitivity of 85.7% (95% confidence interval, 56.2-97.5), specificity of 90.6% (73.8-97.5), positive predictive value of 80% (51.4-94.7), negative predictive value of 93.5% (77.2-98.9), and accuracy of 89.1% (75.6-95.9). Ten adverse events related to puncture and aspiration occurred in 5 (9.6%) of 52 patients; there were no endoscopy-related adverse events. In our study, the largest to date, endoscopic sampling compared favorably with puncture and aspiration for identifying H. influenzae, M. catarrhalis, and S. pneumoniae in ABMS and produced less morbidity.