Buccal mucosa carcinoma has an aggressive nature of spreading into the adjacent masticatory space resulting in difficulty in mouth opening and hindering adequate clinical examination by visualization. Buccal mucosa carcinoma proves a diagnosing challenge to the clinician due to its rapid metastases into the adjacent tissues. Such a case of buccal mucosa carcinoma in a 40-year-old male, who reported with a chief complaint of restricted mouth opening and inability to eat, is presented here. This article also enlightens the importance of PET-CT scan in the diagnosis of buccal mucosa carcinoma with severe trismus.