The prevention of diabetes and its complications is a challenge for the healthcare team. The aim of this study was to evaluate the effect of educational action on the disease knowledge of patients with type 2 diabetes. A randomized clinical trial was conducted with 62 patients registered in a service of reference in the treatment of hypertension in 2010. Data were collected through a questionnaire applied to the Intervention (IG) and Control (CG) groups at the beginning and at the end of the study. The IG participated in group educational activities, using problematization methodology. The results showed a significant increase in knowledge about diabetes in the patients of the IG, in all the topics (p<0.05). In the CG, some changes were observed in knowledge, however, these were fewer when compared with the IG. In conclusion, it was possible to increase disease knowledge through the performance of educational activities. Clinical trial identifier: RBR-58n26h