The objective was to determine the frequency and characteristics of medication errors (ME) presented in inpatient service of a clinic in Cali, Colombia. Were recorded in the pharmacotherapeutic profile and demographic data related to patient medication. From the review of the medical prescription, and pharmacotherapeutic profile nursing kardex verified the presence of ME. We performed a descriptive analysis, bivariate and multivariate between ME and each of the variables. Information is captured 144 patients, identifying ME 31, for a frequency of 10%, 23 ME / 100 patients, 5 ME / 100 stays and 2 ME /100 days of medication. The ME most frequent was of omission of the drug, the process where was generated in the dispensation, were those most committed and pharmacy assistants who detected it was more nurses. Bivariate analysis showed that the opportunity to submit a ME among those hospitalized more than 6 days was 5 times compared to those that are less time. Perform pharmacotherapy follow EM identified and anticipate the generation of adverse drug events.