Pericardial cysts are rare anomalies of the pericardium that are usually asymptomatic and followed by two-dimensional (2D) echocardiography. Here we report a large pericardial cyst that could not be measured accurately by 2D echocardiography but three-dimensional (3D) echocardiography enabled measurements of the cyst that correlated well with computed tomography measurements. In addition, 3D echocardiography demonstrated the mono-trabeculated nature of the cyst further suggesting the incremental value of 3D echocardiography in the evaluation of pericardial cysts. The cyst was subsequently resected surgically. © 2012, Wiley Periodicals, Inc.