ObjectiveThe emotional status of patients with diabetes mellitus (DM) is important in the course of treatment. The present study aimed to determine the level of loneliness among patients with DM and to evaluate the relationship between the patients’ level of loneliness and medication adherence.MethodThis cross-sectional study used a semi-structured questionnaire and the University of California, Los Angeles Loneliness Scale to collect data from 325 patients who were diagnosed with DM.ResultsWe found that loneliness scores were significantly elevated in individuals with a low level of education, unmarried individuals, and students. Furthermore, these scores were elevated in patients diagnosed with type 1 DM, patients on insulin therapy, patients diagnosed with diabetic foot syndrome, patients who did not exercise regularly, and patients who reported being disturbed by reminders from their families or spouses to take their medications or they did not feel anything after such reminders.ConclusionsIndividuals with DM may encounter various problems in their daily lives. Evaluating the emotional status in these individuals, including loneliness and treatment adherence, is important in ensuring that their needs are being met.