OBJECTIVE: A study about the adherence of the antimicrobial prescriptions to the local guidelines of treatment of infections was conducted in a hospital emergency department to study the clinical and epidemiological characteristics of the patients who received these treatments. Conducting a feasibility study for supporting the design and execution of future studies, addressing specific aspects of the appropriateness of the antimicrobial prescription. METHOD: Observational, descriptive and cross-sectional pilot study, with retrospective data collection about the antimicrobial prescription in a hospital emergency department. Seven cross sections were made, corresponding to 7 different days of the week, in 7 consecutive weeks. INCLUSION CRITERIA: patient over 14 years of age, with at least one first dose of antimicrobial treatment prescribed on the day of recruitment. The main variable was the inappropriate antimicrobial prescription according to the local guidelines. Epidemiological and clinical parameters of the patients were collected as secondary variables. In order to determine inappropriate prescription a revision was carried out by 2 specialists in emergencies, 2 pharmacists and one specialist in infectious diseases, all unrelated to prescriptions. RESULTS: One hundred sixty eight patients with 192 prescriptions were evaluated. 76 (39.6%) of the prescriptions were not conformed to the local treatment guidelines. Of these, 55% were with active antimicrobial coverage against the microorganism but not recommended, 23.5% with inactive drugs, 13.7% presented an inappropriate dose and 7.8% were unnecessary treatment. The strength of agreement in the evaluation of the adequacy of treatment between doctors and pharmacists was high (kappa=0.71). CONCLUSIONS: A high rate of inappropriate antimicrobial prescriptions was obtained in a hospital emergency department according to local guidelines. The hospital pharmacist has an opportunity to improve the use of antimicrobials in this area.