The aim of this paper is to analyse how medication incidents are detected in different phases of the medication process. The study design is a retrospective register study. The material was collected from one university hospital's web-based incident reporting database in Finland. In 2010, 1617 incident reports were made, 671 of those were medication incidents and analysed in this study. Statistical methods were used to analyse the material. Results were reported using frequencies and percentages. Twenty-one percent of all medication incidents were detected during documenting or reading the documents. One-sixth of medication incidents were detected during medicating the patients, and approximately one-tenth were detected during verifying of the medicines. It is important to learn how to break the chain of medication errors as early as possible. Findings showed that for nurses, the ability to concentrate on documenting and medicating the patient is essential.