Angle Class III malocclusions are not so frequently met but they raise big problems of treatment. The analyzed case represents a 14-year-old patient that came to the dental consulting room with an Angle Class III malocclusion determined by the excess of the somatotropic pituitary hormone and a gingival hyperplasia more emphasized at the level of inferior frontal teeth. The patient followed a fixed appliance treatment, the straight-wire technique. All along the treatment and after it, the hyperplasia and the gingival inflammation not only maintained but they even got worse. Thus, an improper hygiene associated with a severe Angle Class III malocclusion maintains and aggravates the gingivitis. The histological and immunohistochemical study of the gingiva revealed important epithelial modifications that led to an epithelial hypertrophy with a tendency toward acanthosis and to severe epithelial erosions. An inflammatory chronic process (rich in lymphocytes, plasma cells and macrophages full of angiogenesis vessels) and an intense reaction of the fibroblastic cells appeared in the gingival corium.