The appropriateness of drug prescription is objective of the National Health System for the sanitary and economic repercussions linked. The main objective of this paper is to analyze the appropriateness of drug prescription on patients 65 years or older and identify the most prevalent prescribing errors. Observational, descriptive, transversal, multicenter study in Health Centers doctors in training in Cáceres. 471 patients 65 years or older were included by convenience samplin.The sample size was calculated to an accuracy 3.5%-5% and a confidence level 95%. The measured variable was the criteria STOPP/START. We calculated mean and standard deviation for quantitative variables and relative frequencies for qualitative variables. The most frequent STOPP criteria were: duplication of drugs (9.76% CI 95% 7.40 to 12.78), prolonged use of long-acting benzodiazepines (7.22%, 95% CI 5.21 to 9, 92) and the use of aspirin in patients without cardiovascular secondary prevention (7% 95% CI 5.03 to 9.68). The most frequent START criteria were: omission of antiplatelet agents and statins in diabetes coexisting one or more cardiovascular risk factors (9.34 and 7.03 to 12.31% 95% 95% 4.46% 2.93 to 6, 72), calcium and vitamin D in osteoporosis (5.31%, 95% CI 3.61 to 7.72) and metformin in type 2 diabetes metabolic syndrome ± (4.46%, 95% CI 2.93 - 6.72). The main inappropriate prescribing concerns treatments that should be suspended or modify. The duplications were the most common cause of inappropriate prescribing, being more frequently involved drugs like benzodiazepines, NSAIDs and drugs in drugs associations. The second cause of inadequacy most prevalent was the prescription of benzodiazepines with long half life. The third most common cause was acetylsalicylic acid, both through overuse or omission.