The electrocardiogram (ECG) is essential for the diagnosis of some potentially life-threatening and time sensitive conditions, such as ST-elevation in myocardial infarction (MI). It is therefore imperative that healthcare professionals responsible for performing and interpreting ECGs are alert to the features of lead misplacement, as these can alter the ECG appearance dramatically, resulting in unnecessary investigations, admission to hospital, and treatment. ECG lead misplacement can result in significant harm to the patient if essential treatment is withheld or if the incorrect treatment is delivered solely on the basis of ECG findings. Case report: An unusual and previously unreported case of misplacement of all 12 ECG leads is presented, which would have resulted in significant harm to the patient had it not been identified so early. Conclusion: The ECG is one of the most important and most frequently requested investigations in the management of the acutely ill patient. A review of ECG lead misplacement is presented.