ObjectivesOral lichen planus, a chronic inflammatory immune disease, occurs in the oral mucosa. We aimed to assess the prevalence and possible influencing factors of oral lichen planus in patients with diabetes mellitus.Subjects and MethodsThis cross‐sectional study involved 525 patients with diabetes mellitus and 525 controls. We collected information on blood glucose level, duration of diabetes, diabetic complications, treatment methods, other systemic diseases and medication history.ResultsOral lichen planus was significantly more prevalent in the diabetes mellitus/type 2 diabetes mellitus group than in the controls (2.3%/2.2% vs. 0.6%, p = 0.019/0.022). There was no significant association between patients with diabetes mellitus with and those without oral lichen planus in age (p = 0.195), sex (p = 0.390), blood glucose level (p = 1), duration of diabetes (p = 0.638), diabetic complications (p = 1), treatment methods (p = 0.962), other systemic diseases (p = 0.891) and medication history (p = 0.848).ConclusionsDiabetes mellitus was associated with oral lichen planus; there was a higher prevalence of oral lichen planus in patients with diabetes mellitus/type 2 diabetes mellitus than in those without diabetes. Oral lichen planus development in patients with diabetes mellitus was not significantly associated with age, sex, blood glucose level, duration of diabetes, diabetic complications, treatment methods, other systemic diseases and medication history.