The mistakes in the system of utilization of medicines (SUM) are a clinical problem that increases the morbidity - mortality in the hospitals and the cost of the treatment. The aim of the work was to detect the mistakes in the SUM, to establish the factors associated to his occurrence and his relation with the adverse event, in patients hospitalized with high pharmacological risk, in a hospital of the third level of Bogota; in a period of three months of the year 2012. Method: Direct observation was realized in 318 adults, the review of their clinical records in 309 of them and the review of the voluntary reports of adverse events related to medicines. The analysis of results was realized across descriptive statistics by Stata 10. Results: Thinking that the global prevalence of mistake for every 100 patient doses, in the whole system of utilization of medicines was 5 % or more in 95 % of the patients; the lack of round of pharmacological safety with 94.03 % and the omission mistake of the record after the administration of the medicine with 68.62 % were the observed mistakes, which occupied the first place in field and review of clinical histories respectively. Of the total of analyzed mistakes, 1.89 % managed to damage the patient. Conclusions: The shifts in the morning and the weekend, the experience of the personnel of minor infirmary to 6 months, and the stay at hospital longer than 10 days were circumstances where the prevalence of mistakes was high. The nurse has the responsibility of controlling de development of each period of the SUM and to lead its continuous improvement.