Background: Medication errors occur frequently. Studies assume that up to 30% of care recipients are exposed to a possible medication error. Specific medication errors include taking the wrong doses or quantities of medication as well as omitting medication. For the outpatient sector, the study situation regarding such errors is limited. Therefore, it was investigated how often medication errors occur or have been reported and whether they are related to training, quality assurance measures and other structural conditions of outpatient care services. Methods: A Germany-wide cross-sectional study was conducted in the winter of 2016/2017 among care employees of outpatient care services. A total of 107 outpatient care services with 656 employees were included in the study. Within the framework of logistic regressions, correlations were investigated between errors committed and errors reported in terms of the years of work experience, completed medication training, the type of employment, geographical location of employment, application of the dual control principle, and the number of patients per shift. Results: A total of 107 outpatient care services could be included in the study, with 656 employees. Of 413 fully qualified nurses, 48.9% stated that they had themselves made an error in a 12-month period. Of all care workers questioned, 30.2% said they had reported errors, with 127 people providing no information on this issue. Provided that nurses had attended medication training within the last two years, the odds of not making medication-related errors were almost twice as high (odds ratio (OR) 1.79; confidence interval (CI) 1.42 - 3.09). Whenever nursing staff applied the dual control principle, the odds of not making a mistake were more than three times higher (OR 3.13; IK 1.88-5.20) than when the principle was not applied. The odds of reporting an error were almost twice as high (OR 1.92; IK 1.18-3.13) when the dual control principle was used compared to when it was not used. Conclusion: Medication-related errors occur frequently in outpatient care. Regular training and adequate quality management measures (e.g. application of the dual control principle) can help to make the medication process safer for everyone involved in outpatient care.