Coronoid process hyperplasia (CPH) is a rare condition that causes trismus. No definite symptoms would be noticed by patients until decrease in mouth opening. We report three cases which received surgical intervention through intraoral coronoidectomy/coronoidotomy followed by postoperative mouth opening physiotherapy within a week after operation. Satisfactory results for the first and second cases, but only mild improvement for the third one. Due to rarity of the condition, the diagnosis of CPH should not be overlooked and be included in the list of differential diagnosis when dealing with trismus.