Aims: This study aimed to determine the association between the level of acceptance of illness and medication adherence, metabolic control, and risk of diabetic foot in patients with diabetes. Methods: This descriptive study was conducted with 298 patients with diabetes. The questionnaire comprised the demographic characteristics of the patients, Modified Morisky Scale and the Acceptance of Illness Scale. The study data were collected by the researchers through direct interviews using the questionnaire. Results: Acceptance of illness in patients with diabetes was statistically significantly higher in the group with a higher level of knowledge of medication adherence (p < 0.001). Moreover, the acceptance of illness had a statistically significant negative correlation with fasting plasma glucose (r = −0.198; p < 0.001) and glycated hemoglobin (r = −0.159; p = 0.006) levels in individuals with diabetes. Levels of acceptance of illness had a statistically significant association with the risk of diabetic foot (p < 0.01). Conclusions: The study found that the level of acceptance of illness was associated with the level of knowledge about medication adherence, metabolic control, and risk of diabetic foot in individuals with diabetes. It may be recommended to conduct clinical trials to determine the effect of evaluating the level of acceptance of the illness on diabetes management and to increase this level.