Background: The correct injection technique is crucial for people with insulin therapy. However, barriers to insulin injections exist, which can lead to problems with injections. In addition, injection behavior may deviate from recommendations leading to lower adherence to the correct injection technique. We developed two scales to assess barriers and adherence to the correct technique. Methods: Two item pools were created to assess barriers to insulin injections (barriers scale) and adherence to the correct technique (adherence scale). In an evaluation study, participants completed the two newly created scales, as well as other questionnaires used for criterion validity. Exploratory factor analysis, correlational analysis, and receiver operating characteristics analysis were computed to analyze the validity of the scales. Results: A total of 313 people with type 1 and type 2 diabetes using an insulin pen for insulin injections participated. For the barriers scale, 12 items were selected achieving a reliability of 0.74. The factor analysis revealed three factors namely emotional, cognitive, and behavioral barriers. For the adherence scale, nine items were selected achieving a reliability of 0.78. Both scales showed significant associations with diabetes self-management, diabetes distress, diabetes acceptance, and diabetes empowerment. Receiver operating characteristics analysis showed significant area under the curves for both scales in classifying people with current skin irritations. Conclusions: Reliability and validity of the two scales assessing barriers and adherence to insulin injection technique were demonstrated. The two scales can be used in clinical practice to identify persons in need of education in insulin injection technique.