Introduction: Carcinogenesis is associated with complex changes in metabolism, which include increased consumption of glucose, by breakdown of glycogen and the tumor cells. This may be related to increased blood glucose level in patients with malignant or premalignant diseases. Adverse oral habits like smoking and tobacco chewing are common etiological factors related to oral premalignant diseases. The association of these factors may be related to an increased blood glucose level as an early biomarker for malignancy in suspected patients. Objective: The purpose of this study is to establish a relationship between blood glucose levels and potentially malignant oral disorders in patients with a long-term history of tobacco chewing, smoking, or both. Method: This study was conducted among 30 patients in 1) Persons with clinically developed PMD and a >5-year history of tobacco chewing or smoking or both, 2) Persons with no clinically developed PMD but a >5-year history of tobacco chewing or smoking or both formed the subjects while 3) 30 persons with clinically normal appearing oral mucosa and no tobacco history formed the control group. Results: Results showed that the overall RBS level was increased with habit and with lesions. The male population showed a greater increase. RBS was prominently increased in the male population with OL (139.8 gm/dl) compared to males with no habit history (114.9 gm/dl). Conclusion: The present study suggests a possible association of RBS with OL, while the association with OSCC was not significant. Palabras clave: Tobacco, carcinogenesis, oral leukoplakia, oral squamous cell carcinoma, random blood sugar