Background— We investigated diastolic mechanical dyssynchrony and its relation to clinical status in pediatric dilated cardiomyopathy (DCM). Methods and Results— We calculated a diastolic and systolic dyssynchrony index (standard deviation of time to peak tissue early diastolic/systolic velocity in 12 left ventricular segments) in 33 children with DCM and 46 control subjects. A threshold to diagnose diastolic dyssynchrony was determined, and cardiac function and clinical outcomes were compared between DCM patients with and without diastolic dyssynchrony. Left ventricular wall motion was more synchronized in diastole than in systole. The diastolic dyssynchrony index was significantly higher in children with DCM than in control subjects (28.1�18.1 versus 9.1�3.8 ms, P <0.0001). A 17-ms threshold indicated the presence of diastolic dyssynchrony. Patients who died or underwent transplantation had greater diastolic dyssynchrony (diastolic dyssynchrony index 37.9�20.5 versus 22.1�13.8 ms, P =0.01), and the rate of transplant-free survival appeared to be worse for DCM patients with diastolic dyssynchrony than for patients with synchronous DCM (hazard ratio 2.98, P =0.11; hazard ratio adjusted for disease duration 2.95, P =0.17). Conclusions— Left ventricular diastolic mechanical dyssynchrony is common in pediatric DCM, especially in patients who subsequently experience transplantation or death, and may be associated with a decreased length of transplantation-free survival.