Introduction: According to the WHO, diabetes is a chronic disease that occurs when the pancreas does not produce enough insulin or the body does not effectively use the insulin it produces. Objective: Design an instrument that allows for the assessment of nursing performance in Diabetes Mellitus in primary care. Method: Research with a quantitative approach, experimental, descriptive, and transversal design. Development of an instrument to determine its reliability and content validity. The sample used for the evaluation of internal reliability was made up of 10 patients diagnosed with diabetes mellitus who are treated in the health centers of zone 3 belonging to the Pelileo Canton, Province of Tungurahua, who agreed to collaborate with the research, to check the understanding of the questions and the operation of the instrument. Internal consistency was determined by calculating Cronbach's Alpha coefficient. Results: Expert professionals in diabetes mellitus assessed the pertinence, relevance, and clarity of the 20 items divided into four dimensions, qualifying them as applicable. The internal consistency of Cronbach's Alpha was 0.97, which demonstrates that the formulation of the items is reasonable, satisfactorily defined, and suitable in the presence of the questionnaire. Conclusions. The results obtained to evaluate the instrument and the application of the pilot test were adequate. This valid and reliable instrument justifies its use in the research field. The instrument is easy and quick to apply, allowing us to know the perception of patients with Diabetes Mellitus about the care received by the nursing staff in the PHC.