Improper placement of recording electrodes on the skin can generate misleading patterns on the electrocardiogram (ECG). The alterations in the normal ECG caused by lead misplacement were reviewed. Although most clinicians can recognize the common right arm/left arm lead switch that imitates a nonsinus atrial rhythm with high anterolateral myocardial infarction, many other errors are possible. Less common lead placement errors are often difficult to detect. Exchanging the right arm and left leg leads creates what seems to be an inferior wall myocardial infarction and a nonsinus atrial rhythm in normal patients. Reversal of the right arm and right leg connections creates a unique pattern of diffuse low voltage in the limb leads. Precordial lead switches are common and can be recognized by the abnormal R wave progression that is created.