Postsurgical follow-up information was obtained on 64 dogs with 69 histologically well-differentiated melanocytic neoplasms that involved the mucous membranes of the lips and oral cavity. The patients received no adjunct therapy. Sixty one of 64 dogs (95%) were alive at the end of the study or had died of causes unrelated to the tumor, with a mean survival of 23.4 months and a median survival of 34 months after surgery. Twenty-eight dogs alive at the end of the study had a mean survival of 31.3 months after surgery. There were 2 dogs, which had recurrent tumors, that were still alive at the end of the study. All dogs that died of tumor-related causes (3) and all dogs with recurrent tumors (2) had tumors in the oral cavity. Results of this study indicate that a favorable clinical course and prolonged survival can be expected in most dogs with histologically well-differentiated melanocytic neoplasms of the mucous membranes of the lips and oral cavity, with only local excision of the lesions and no adjunct therapy.