Several disparate mucocutaneous diseases present oral mucosal lesions that have been classically labeled as "pre-cancerous", "pre-malignant", or "potentially malignant". These include oral lichen planus, dyskeratosis congenita, tertiary syphilitic glossitis chronic graft-versus-host-disease, and oral discoid lupus erythematosus. There is much confusion in literature regarding the real malignant potential of these oral lesions in relation to the incidence of squamous cell carcinoma. We tried to unify the occurrence of squamous cell carcinoma in some oral mucosal diseases into the classic concept of "Marjolin ulcer". We analyzed the most relevant published evidence of the occurrence of squamous cell carcinoma arising in oral lichen planus, dyskeratosis congenita, tertiary syphilitic glossitis chronic graft-versus-host-disease, and oral discoid lupus erythematosus, and tried to establish a logical link between them. Reported cases of squamous cell carcinoma occurring in oral lesions of these diseases seem to appear in old standing, scarring lesions. Oral lichen planus, dyskeratosis congenita, tertiary syphilitic glossitis, chronic graft-versushost-disease, and oral discoid lupus erythematosus are not "pre-malignant diseases", their long-lasting mucosal scars are prone to the development of squamous cell carcinomas. In this sense, this tumor can be considered a mucosal type of Marjolin ulcer.