<b><i>Objective:</i></b> Left atrial (LA) mechanical function is thought to be virtually inexistent in patients with permanent atrial fibrillation (AF). Due to recent advances in multidetector computed tomography (MDCT) technology, it is now possible to acquire images of the entire heart in a single heartbeat. The objective of this study was to compare individual components of LA function assessed by MDCT in patients with permanent AF and patients in sinus rhythm (SR). <b><i>Methods:</i></b> 320-slice MDCT was performed in 30 patients with permanent AF. Measurements of LA volumes during the cardiac cycle were compared to 30 patients in SR, who were matched with respect to age, sex, left ventricular ejection fraction and body surface area. <b><i>Results:</i></b> LA volumes were significantly larger in patients with AF than SR patients at all times during the cardiac cycle (LA maximal volume; 82 vs. 55 ml/m², p < 0.0001, LA minimal volume; 71 vs. 30 ml/m², p < 0.0001). However, except for the absence of active LA emptying, the overall trend of the LA time-volume curve was similar in patients with AF and SR. <b><i>Conclusion:</i></b> Compared to SR patients, patients with permanent AF have significantly increased LA volumes throughout the cardiac cycle. Yet, a residual hemodynamic role of LA function may be maintained during permanent AF.