Masseter hypertrophy is a benign condition characterized by unilateral or bilateral enlargement of the masseter muscles, which was first described by Legg in 1880. The highest incidence of this condition is in the second and third decades of life with no gender predilection. The etiology in the majority of cases is unclear. However, most cases have a clenching or grinding habit, and other conditions such as temporomandibular joint disorders, bruxism, and malocclusion have also been suspected as causative factors for this condition. Other factors include unilateral chewing due to loss of teeth or dental pain, congenital atriovenous fistula, or focal dystonia. This paper describes a case of idiopathic unilateral masseter muscle hypertrophy in a 40-year-old male, reviews the literature, and proposes effective treatment options.