Immunological disorder-related oral lesions are relatively uncommon in adolescence; however, the condition is chronic and difficult to cure. This retrospective study aimed to examine the distribution of oral lesions related to immunological disorders in Northeastern Thai Oral Pathology Databases. The data were retrieved from the Oral Pathology Databases of the Faculty of Dentistry, Khon Kaen University, during 2000-2019. A total of 1,858 lesions with histopathology data derived from patients aged between 16-35 years were analyzed. Among these, 56 lesions (3%) were diagnosed as related to allergic/immunological disorders, with no preference on sex ratio (p=0.36). The prevalence of immunological oral lesions was increased with age (p<0.001). However, oral lichen planus (62.5%), pemphigus vulgaris (14.3%), and benign mucous membrane pemphigoid (BMMP) (5.3%) that are commonly reported in the middle-aged patients were found in the samples aged 20 years and under. The most common site was buccal mucosa (66.7%), followed by gingiva (20.6%). Findings from this study have provided a glimpse into the prevalence and distribution of immunological oral lesions in the early adulthood population from one of the largest databases in Thailand. The information indicated that oral health screening for early adulthood should include a thorough examination of the soft tissue. It is very important that these lesions should be early diagnosed and treated appropriately to minimize the risk of turning into malignancy, leading to a better prognosis and improved quality of life for the patient.