The presence of mucogingival deformities often have an impact on patients in terms of esthetics and function. The variety of the conditions makes it difficult to place gingival and alveolar mucosa deformities under a single definition. Mucogingival deformities, as defined in this paper, may be congenital, developmental, or acquired defects. These may occur around natural teeth or implants and in edentulous ridges. They may be localized to soft tissues or be associated with defects in the underlying bone. They may show different degrees of severity and extension. A classification of mucogingival deformities should provide a method for identifying the different conditions in order to improve diagnosis, etiologic identification, research, treatment, and insurance evaluation. Ann Periodontol 1999;4:98‐100.