Self-management of diabetes is encouraged; however, it is not an easy task and requires a good understanding of the disease. To determine how to improve the self-management abilities of diabetes in people with an intellectual disability (ID), this study explored the knowledge and understanding of diabetes held by a select group of adults with diabetes. The group was made up of 14 adult New Zealanders (eight males and six females; age range 23–69 years) with type 1 diabetes (n = 6) and type 2 diabetes (n = 8). They and their nominated key informants were interviewed. Blood sugar levels (gained from using hemoglobin A1c (HbA1c) tests) were obtained on all participants. HbA1c levels ranged from 5.4% to 12.3%. The participants fell into three categories of understanding diabetes: (1) those who had a good understanding of the disease; (2) those who had some knowledge but their actual understanding was limited; and (3) those who demonstrated only a very basic knowledge. It was found that all of the adults were actively engaged in the self-management process, and all appeared to have some understanding of the role of diet, blood sugar levels, and exercise in the management of their disease. Support from others was important in this process, even for those adults who had a good understanding of the disease. Diabetes significantly impacted the adults' lives, and in some cases, prevented them from living independently. When interviewed, the adults suggested strategies to assist with self-management such as the use of a “buddy” system to encourage exercise. Authors concluded that adults with ID can be engaged in self-management of their diabetes. However, it is important that they continue to receive education and support throughout their lives and that time be spent with each individual to identify how to provide the best education and support. Peer-led education and user-friendly resources are recommended to achieve lifelong education and support.