The healing of the secondary epithelization vestibuloplasty wound was studied in five dogs. Special attention was paid to the nature of the relapse. Clinical records by means of tattoo marks and tracings at the time of operation and follow-up examination show that the loss and regain of sulcus extension follow the pattern of healing of an excision wound. The attachment of new mucosa (gained from secondary epithelization of the periosteum) to the bone eventually becomes loose in the muscle bearing region of the jaw. The detached muscles reinsert into scar tissue near their preoperative attachment. Thus, the relapse seems to be the result of an interaction of wound contraction, loosening of new mucosa and muscle reattachment. The findings are discussed in the light of recent concepts of wound healing. Techniques implying a grafting of skin or mucosa to the periosteal wound are advocated as a logical approach to the prevention of a relapse.