Left atrial (LA) enlargement is associated with atrial fibrillation (AF), but new-onset AF often occurs in the absence of LA enlargement. AF may be related to myocardial fibrosis, and even though left ventricular fibrosis is associated with mechanical dispersion, this phenomenon is not well studied in AF. We hypothesized that detection of LA dysfunction and mechanical dispersion using strain echocardiography is useful for predicting new-onset AF.Baseline echocardiography was performed at entry in 576 community-based participants at risk of heart failure or AF. In this case-control study, we compared 35 individuals with new-onset AF (age 70 ± 4 years; 57% men) over 2 years of follow-up with 35 age- and sex-matched individuals who did not develop AF from the same cohort. Using speckle-tracking echocardiography, we measured the LA strain in each of 12 segments in the two- and four-chamber views. LA mechanical dispersion was defined as the SD of time to peak positive strain corrected by the R-R interval (SD-TPS, %).There was no significant difference in LA volume index (32.5 ± 9.2 mL/m vs 29.5 ± 8.3 mL/m; P = .16); patients with new-onset AF had significantly worse LA pump strain (16.6% ± 4.3% vs 20.6% ± 4.3%; P < .01) and reservoir strain (31.4% ± 7.7% vs 38.0% ± 7.3%; P < .01) than those without AF. SD-TPS was significantly higher in patients with AF than in those without it (6.3% ± 2.3% vs 3.9% ± 1.6%; P < .01). SD-TPS was independently associated with new-onset AF after adjustment for patient characteristics, LA volume, and strain (hazard ratio = 1.26; 95% CI, 1.10-1.45; P < .01). In the nested Cox models, the model based on the LA volume and strain for predicting new onset AF was significantly improved by adding SD-TPS (P < .01).2LA dispersion obtained from strain echocardiography seems to provide incremental information about LA volume and function in the prediction of new-onset AF and warrants testing in a larger study.