Arterial hemoglobin oxygen saturation was prospectively monitored in 103 consecutive patients undergoing office colonoscopy to determine the incidence of any clinical characteristics which might predict arterial desaturation to less than 90%. Baseline saturations were obtained prior to premedications and continuously during the examination using a finger mounted pulse oximeter. Intravenous premedication regimens varied from none to a maximal dose of 50 mg of meperidine and 10 mg of diazepam. All colonoscopies included cecal intubation and were performed by one investigator employing a video colonoscope. The incidence of desaturation was 41% without significant variation among the sedation groups. Age was positively correlated with desaturation (p less than 0.05). Sex, obesity, history of lung or heart disease, chronic cardiac medications, and baseline saturation percentage failed to be sensitive predictors of desaturation. No parameter could be correlated with prolongation of desaturation below 90%. No adverse outcomes or complications were noted during the periendoscopy period, suggesting that oximetry monitoring during outpatient colonoscopy may not be clinically useful.