In recent years, medication error has received considerable attention because it causes substantial mortality, morbidity, and additional health care costs. Collecting information in this field depends on the willingness of health professionals to report their errors. Another important point is to identify patients at high risk for an adverse drug event (ADE) to oversee the quality of the entire drug distribution chain, including prescription, drug choice, dispensing, and preparation to the administration of drugs. To assess the prevalence rate of ADEs. To ascertain those related to medication errors to develop prevention strategies. Prospective cohort study. Multicenter study, 7 intensive care unit in academic and military hospital of Rabat. Three months. Adult and pediatric patients in medical/surgical intensive care units. COLLECTION DATA: One coordinator for each participating ward collaborates with a pharmacist investigator from Moroccan pharmacovigilance center in the detection of ADEs. Of the 696 patients studied, the investigators identified 108 incidents (15.5 %) (95% confidence interval, 14.1-16.9). The reviewers concluded that 56 (70%) of 80 ADEs were nonpreventable, which, by definition, are considered as ADRs. Among the 52 medication errors, 28 (53.8%) led to potential ADEs and 24 (46.2%) led to actual preventable ADEs. There were 7.7 medication errors for 1000 patient-days. We noted that the preventable ADEs occurred in the prescribing (71.1%), administration (21.2%), transcription (5.7%), and dispensing stages. Errors of wrong or improper drug use accounted for the majority of potential and actual preventable ADEs (23%), followed by improper dose (21.1%), wrong duration of treatment (19.2%),wrong rate of administration(13.5), errors due to drug omission (9.6%), wrong administration technique (5.8%), wrong dosage form (3.8%), and wrong administration timing (1.9%). This study argues the need for pharmacovigilance to extend its scope to medication errors to improve the safety of drugs. Our results underlined that medication errors are likely to be more serious than ADRs. Our approach based on the collaboration between the pharmacovigilance center and clinicians can be a powerful tool for incorporating error reporting into the culture of medicine.