This study identified and analyzed the medication systems in 04 university hospitals located in Recife, Ribeirão Preto, Goiânia and São Paulo, Brazil, after approval by the Research Ethics Committee and authorization by the hospital directors. Data were collected through a structured interview with one of the professionals in charge of the medication system and non-participant and direct observation during one week. The results indicated the points requiring improvement, such as the use of abbreviations, lack of standardization in medication administration times, lack of updated and complete information about the patient, the pharmacy's not working 24 hours a day in hospitals and others. 66 phases were shown in Hospital A, 58 in B, 70 in C, and 80 in D concerning the medication system. Simplifying the processes by reducing the number of phases is the key to reducing medication errors.