There is growing interest in using portable monitoring for investigating patients with suspected sleep apnea. Research studies typically report portable monitoring results in comparison with the results of sleep laboratory-based polysomnography. A systematic review of this research has recently been completed by a joint working group of the American College of Chest Physicians, the American Thoracic Society, and the American Academy of Sleep Medicine. The methods for comparing the results of portable monitors and polysomnography include product-moment correlation, intraclass correlation, mean differences/limits of agreement, sensitivity, specificity, and likelihood ratios. Each approach has advantages and limitations, which are highlighted in this review.