A one-day-old full-term female infant with massive "cardiomegaly" developed marked respiratory distress soon after birth. The two-dimensional (2D) echocardiogram demonstrated a 4×5-cm cystic mass adjacent to the left ventricular free wall. Computed tomography (CT) confirmed the presence and dimension of the cyst and CT number indicated the fluid within the cyst to be serous. A pericardial cyst was successfully removed at thoracotomy. Two-dimensional echocardiography and CT, both noninvasive procedures, are fully adequate tools in the diagnosis of pericardial cysts in the neonate, so that invasive investigations may be avoided. © 1987 Springer-Verlag New York Inc.