So far, little is known about drug-related problems in the homecare setting. It is estimated that up to 30% of homecare patients experience a potential medication error, most frequently happening during preparation and administration of drugs. In order to identify error-prone process steps in a Swiss homecare organisation caring for 1854 patients per year, direct observation of the medication use process, including the analysis of 10% of all prescriptions, was executed. Three complimentary methods were combined for the assessment of qualitative aspects of the medication use process: the analysis of a critical incident reporting system, a survey among homecare nurses, and a failure, mode and effects analysis. The medication use process is complex, consisting of 20 individual steps. Patients are prescribed an average of 7.5 ± 3.5 drugs per day, including 1 to 9 doses not suitable for deblistering into weekly dispensing systems. Of 84 reported errors, 74% happened during drug preparation. Communication with physicians, patients interrupting drug preparation and not transmitted changes of the drug regimen were considered the most critical process steps.