The aim. Rationale of methodology for classification of medication related errors during retail sale of medicines in Ukraine.Materials and methods. With the help of system-analytical, statistical, comparative methods of analysis, as well as descriptive and abstract modulation and generalization, we investigated domestic and foreign scientific publications and legal framework.Results. An analysis of the current state of the domestic pharmacovigilance system showed that it provided reports of adverse drug reactions, their lack of efficacy, but no categories characterizing medication errors, in particular during retail sales in pharmacies and self-medication. However, despite the lack of a unified classification of medication errors, it is possible to distinguish the main categories of medication errors and group them by stages of occurrence: error, that occur during the prescribing of medication, the use of drugs during inpatient treatment, and in the release of drugs by pharmacist. The results of the comparative analysis of International classification and medication errors monitoring systems have determined that most of them include error that related to the dose, conditions and duration of medication administration, compliance of the medication with the patient, compliance with the prescribed / recommended pharmacotherapy and adapted accordingly to the conditions of development of health care of different countries.Conclusions. Approaches to the classification of medication errors are generalized and substantiated by the global and national trends in the development of the pharmaceutical sector, the medication error classification model, which can be applied during the retail sale of drugs in Ukraine. The proposed methodology for the classification of medication errors during the retail sale of medications includes 44 categories of errors, which are divided into three levels depending on the stage of providing pharmaceutical assistance: errors in the selection of OTC drugs in the course of consulting by pharmacist, errors in the release of drugs by a pharmacist and errors at the stage of medication use by the patient.