To evaluate whether baseline left atrial (LA) volume and function were associated with clinical or echocardiographic response to cardiac resynchronization therapy (CRT), and to determine LA reverse remodeling as assessed by computed tomography (CT). We prospectively included patients receiving a CRT system who underwent dynamic cardiac CT with measurement of LA size and function before and 6 months after implantation. Patients alive not hospitalized for heart failure, and improving ≥1 NYHA class or ≥10% in 6-min walk test after 6 months follow-up were classified as clinical responders. Echocardiographic response was defined as ≥15% reduction in left ventricular (LV) end-systolic volume. We included 138 patients, of whom 95 (69%) were clinical responders and 114 (83%) were echocardiographic responders. We found no association between baseline measures of LA volume or function and clinical or echocardiographic response. Mean reduction in LA maximum and minimum volumes at 6 months were 3.3 ± 12.7 ml/m(2) (p = 0.004) and 2.6 ± 11.4 ml/m(2) (p = 0.01) corresponding to a relative reduction of 4.1 and 5.0%, respectively. LV end-systolic relative volume reduction was 35.2 ± 22.4% (p < 0.001). No measures of LA function changed significantly. Cardiac CT measures of baseline LA volume and function are not associated with clinical or echocardiographic response to CRT. Change in LA volume and function is marginal after 6 months despite pronounced LV reverse remodeling.