In a series of 100 consecutive patients, the echocardiogram was found to have an accuracy approaching 90 per cent in the diagnosis of pericardial effusion. Analysis of errors and recurring problems revealed 6 pitfalls in interpretation. They are the pulsatile pericardium, the loculated effusion, the uneven distribution of fluid, the overly strong ultrasonic input signal, the impression of extracardiac mediastinal structures, and left pleural effusion.