Medication errors are globally huge in magnitude and associated with high morbidity and mortality together with high costs and legal problems. Medication errors are caused by multiple factors related to health providers, consumers and health system, but most prescribing errors are preventable. This paper is the third of 3 review articles that form the background for a series of 5 interconnected studies of prescribing patterns and medication errors in the public and private primary health care sectors of Saudi Arabia. A MEDLINE search was conducted to identify papers published in peer-reviewed journals over the previous 3 decades. The paper reviews the etiology, prevention strategies, reporting mechanisms and the myriad consequences of medication errors.