New diagnostic and therapeutic technologies are used with growing frequency, improving the quality of medical assistance and increasing life expectancy. Health care, however, is becoming progressively more expensive and complex. Adverse events related to medical assistance, particularly errors, are becoming public, being debated and judged in courts. Given their training, health workers are not prepared to deal with errors, which are associated with shame, fear and punishment. The approach to errors in the health system is usually individualistic, considering such events as acts of insecurity performed by careless, non-motivated and ill-trained persons. The tendency is to hide errors when they occur, with the result that an important learning opportunity is lost. There is another way to deal with errors, a systemic view that has obtained positive results in sectors such as aviation, anesthesiology and unit-dose drug distribution systems. These systems have varied degrees of safety and should take into account human limitations when designed and applied. A change in paradigm is needed when dealing with drugs, as it is not enough for a drug to have quality assurance, but the complete process of drug use should be safe. Medication errors, avoidable by definition, are at present a serious public health issue, leading to loss of lives and significant financial losses. A systemic approach to medication errors may disclose failures in the process as a whole, and improvements can be implemented to reduce their occurrence.