Patterns of rib cage (RC) and abdomen (ABD) motion obtained from a respiratory inductive plethysmograph were studied during disordered breathing events - obstructive apnea, obstructive hypopnea, mixed apnea, and central apnea - in 54 patients with sleep apnea. The type of disordered breathing event was verified by esophageal pressure and bias-flow mask recordings. Obstructive apnea occurred to a variable extent in all patients and was characterized by stereotyped paradoxical motion of the RC or ABD or both in 49 patients (91%). There was no paradox in 2 patients with "feeble" inspiratory effort during obstructions and in 3 patients with normal inspiratory effort during obstructed breaths. The more obese patients displayed paradox of the ABD rather than of the RC. Paradox did not occur in central apnea or in the central component of mixed apnea. Obstructive hypopnea was characterized by paradox during part of the breath. We conclude that RC and ABD motion can adequately characterize apnea in most patients and thus avoid invasive monitoring techniques that can adversely affect sleep. However, if chest wall motion suggests that all apneas are central, a direct measurement of respiratory effort is necessary to exclude obstruction.