Objective: to assess the effect of the preparation plan for hospital discharge on the self-care agency capacity and adherence to treatment in the patients with Diabetes Mellitus treated in the Erasmo Meoz University Hospital (Hospital Universitario Erasmo Meoz, HUEM) during 2019. Materials and methods: a quasi-experimental study, with pre-/post-test assessment in the study group, guided by Dorothea Orem’s theory, with a non-probabilistic sampling of 88 individuals, by convenience. It was conducted by implementing the following instruments: therapeutic conduct, disease or lesion, and scale to assess the self-care agency capacity (ASA); data analysis was performed in Microsoft Excel 2016 and SPSS, version 22.0. Parametric (Student’s t-test for paired samples) and non-parametric (Wilcoxon) statistical tests were also used, considering p-values < 0.05 as statistically significant. Results: the initial self-care agency capacity was 61.48 (low) and the final was 80.43 (fair); therapeutic adherence compliance in the initial assessment was occasionally shown (2.82) and frequently shown at the end (4.38), with both variables showing a statistically significant difference with p-values < 0.05. Conclusions: it was determined that the intervention performed had a positive effect on therapeutic adherence and the self-care agency capacity of the diabetic patients subjected to the intervention.