Aim: The aim of the study was to identify the prevalence of oral mucosal lesions in patients with type II diabetes mellitus (DM). Materials and methods: The present study was a retrospective study which was conducted among patients visiting the outpatient department of a private hospital in Chennai. Patients who were diagnosed with type II DM and presented with no other additional systemic illness who reported to the hospital from June 2019 to March 2020 were included in the study. Oral mucosal alterations were recorded. The collected data was imported into the Statistical Package for the Social Sciences (SPSS) software by International Business Machines (IBM) and analyzed by descriptive analysis and Pearson correlation. Results: The prevalence of oral lesions among the study population of 200 patients with type II DM was 26 (13%). The presence of oral lesions was the most (7%) among the middle-aged population (36–60 years). The male population (52%) showed more prevalence of oral lesions, compared to the females (48%). The most common oral lesion among the study population was lichen planus (32%), followed by angular cheilitis (24%), denture stomatitis (20%), leukoplakia (8%), geographic tongue (8%), and oral candidiasis (8%). Conclusion: Patients with type II DM present with an increased risk of manifestation of oral lesions. The middle-aged population (30–60 years) are at a higher risk of developing oral mucosal lesions, compared to the other age-groups. The most common oral lesion associated with this age-group was lichen planus (30%) and also it was found that males were at higher risk of development of oral mucosal lesions. Clinical significance: Diabetes mellitus (DM) type II is characterized by impaired immune function resulting in various oral lesions. DM causes oral complications which are considered to be major complications of the disease and can decrease the patient's quality of life. Hence, early diagnosis helps in the prevention of complications.