We recently proposed an equation predicting the optimal level of continuous positive airway pressure (CPAP) that abolishes sleep apnea from three simple and easily available parameters: body mass index (BMI), neck circumference, and apnea/hypopnea index (AHI). The present study was designed to validate this equation in a prospective group of patients with sleep apnea returning to the sleep laboratory for CPAP titration study. We studied 26 patients and found that the optimal CPAP was equal to the predicted value in 10 of 26 patients, within +/- 1 cm H2O of the predicted value in another 10 of 26 patients, within +/- 2 cm H2O in four of 26 patients, and outside +/- 4 cm H2O in the remaining two patients. We conclude that (1) optimal CPAP can be predicted to within +/- 2 cm H2O from a few simple measurements, and (2) using predicted CPAP as a starting pressure for CPAP titration, it may be possible to optimize and/or shorten the titration study--a fact with significant implications for reducing the cost of "diagnosis-to-treatment" polysomnography.