OBJECTIVES: To measure ADEs in the elderly due to PIM using standard instruments (Beers Criteria-BC, STOP-START), and related costs in HUA. METHODS: A cross sectional discharges study, obtained results of each instrument (BC, STOP, START) by trained pharmacist, from EHR with CPOE data. Symptomatic ADEs (Near Misses excluded) and PIM prevalence –defined as the proportion (+) screens, for at least one medication indication per discharge. Confounding variables: age, sex, area of admission, poly-pharmacy, ATC group, Diagnosis ICD9CM, ALOS, Charlson S., Katz functional scale, and in-hospital mortality. ADEs prevalence OR (odds ratio) and (95%CI). Stratified and logistic regression analyses (SPPS21), adjusted ADEs (OR _ADJ), discharge costs (I$) per stay (mean, SD; median, quartiles) for ADEs (+) and (-) extracted (U$D 1:Arg$ 8). RESULTS: p<0,05 vs. ADEs (-). Sex, admission site, prior surgery and Katz criteria increased the OR (data not shown, all p<0,05); admission site (wards, ICU, CCU, p trend <0,01).  89 ADEs (15,5%) risk according to BC (+) was OR _ADJ =1,49 (95% CI 1,68-4,66); to STOPP (+) OR _ADJ  1,17 (0,61-2,24); and to START (+) OR _ADJ 0,68 (0,37-1,24) all p>0,05. ALOS risk was OR _ADJ 1,03 (1,005-1,058), p 0,020. Mean I$ ADEs+ = 75 108 U$D (SD 194 515), Median =7 405 U$D; ADEs(-) (N=497): mean 37 866 U$D (SD 88 495), Median = 11 814 U$D. CONCLUSIONS: High PIM prevalence was found, PIM increased ADEs as expected, but short of significance; with a significant effect of covariates; costs and ALOS increase among ADEs + discharges. Larger sample size is required for strict ADEs definition used here.