Background: The aim of the study was to assess the progression of Oral Submucous Fibrosis (OSF) by investigating the correlation between clinical mouth opening and muscle-epithelial distance in tissue sections. Characterization of changes involving muscle was ascertained. Material and Methods: 50 cases and 10 controls were included in this case-control study. Inter-incisal mouth opening was measured and classified according to Lai et al . as Group A (more than 35mm), Group B (30 to 35mm), Group C (20 to 30mm), Group D (less than 20mm). Histopathological sections were graded as very early, early, moderately advanced, advanced OSF. Muscle-epithelial distance was calculated using image analysis software. The four most common degenerative changes observed in muscles, namely fragmentation, highly eosinophilic areas with loss of striations, nucleus internalization and multiple pyknotic nuclei were also assessed. Results: Comparisons of muscle-epithelial distance were made between the clinical and histopathological groups to those of controls. The mean muscle-epithelial distance was: Group A-626.8±309.36 μm, B-827.5±549.72 μm, C-673.2±321.93 μm, D-439.9±173.84μm, Controls-1222.19 ±441.7μm. Post-hoc Bonferroni Test revealed a statistically significant reduction in the muscle-epithelial distance in Group C ( p -value = 0.001) and D ( p -value = 0.001) as compared to controls. The mean muscle-epithelial distance in very early, early, moderately advanced and advanced OSF was 732.73±232.81μm, 726.54±361.63 μm, 548.36±273.13 and 172.40±58.41 μm respectively. Highly significant difference in muscle-epithelial distance was seen between controls as compared to early ( p - value =0.002), moderately advanced ( p -value = 0.001) and advanced OSF ( p -value = 0.001. Fragmentation and highly eosinophilic areas were invariably noticed in advanced OSF. Multiple pyknotic nuclei were variable with no specificity. Conclusions: Reduction in muscle-epithelial distance may prove to be a significant predictor of OSF progression. Degenerative changes must be noted while observing OSF cases, irrespective of the histopathological grade.