Older people are a heterogeneous group of patients, often with multiple comorbidities for which they are prescribed a large number of drugs, leading to an increased risk of adverse drug reactions (ADR) and drug interactions. This risk is compounded by physiological age-related changes in physiology, changes in drug pharmacokinetics and pharmacodynamics, as well as by disease-related, functional and social issues. Inappropriate prescription of drugs is common in the older individuals and contributes to the increased risk of ADR. Several tools have been developed to detect potentially inappropriate prescription, the most frequently used in Spain being Beers' criteria. However, the value of these criteria is limited, especially as they were developed in a different healthcare system. In this article, the Spanish version of a new tool to detect potentially inappropriate prescriptions-STOPP (Screening Tool of Older Person's Prescriptions) and START (Screening Tool to Alert doctors to Right i.e. appropriate, indicated Treatment) criteria-is presented. The creation, development, reliability, and use of these criteria in routine practice is described and discussed. These criteria have shown better sensitivity than Beers' criteria in detecting prescription problems and have the added value of being able to detect not only inappropriate prescription of some drugs, but also the omission of well indicated drugs. The STOPP/START criteria could become a useful screening tool to improve prescription in older people.