Abstract Background Medication errors (ME) are an important problem in all hospitalized populations, especially in intensive care unit (ICU). The aim of the study was to determine incidence, type and consequences of ME. Materials and methods Prospective observational cohort study during six weeks in a Moroccan ICU. Were included all patients admitted for > 24 hours. ME were collected by two reviewers following three methods: voluntary and verbally report by medical and paramedical staff, chart review and studying prescriptions and transcriptions. Seriousness of events was classified from Category A: circumstances or events that have the capacity to cause error, to Category I: patient's death. Results 63 patients were eligible with a total of 509 patient-days, and 4942 prescription. We found 492 ME, which incidence was 10 per 100 orders and 967 per 1000 patient-days. There were 113 potential Adverse Drug Events (ADEs) [2.28 per 100 orders and 222 per 1000 patient-days] and 8 ADEs [0.16 per 100 orders and 15.7 per 1000 patient-days]. MEs occurred in transcribing stage in 60%cases. Antibiotics were the drug category in 33%. Two ADEs conducted to death. Conclusion MEs are common in Moroccan medical ICU. These results suggest future targets of prevention strategies to reduce the rate of ME.