T here have been few large series of mucoceles reported in the literature. Although Thoma and GoldmanlG state that mucocelcs are cysts lined with ductal epithelium and that they are caused by obstruction of the duct of a mucous gland, Bhaskar and associates2 failed to demonstrate an epithelial lining in any of their nineteen cases of mucoceles. Mpiller12 examined histologically nineteen out of a series of forty-four clinical cases and found an epithelial lining in only one. In a series of ninety-seven cases, Standish and ShafeF found epithelial linings in four cases. Chaudhry and colleagues3 reported sixty-six cases, in none of which was there an epithelial lining. The present series of eighty cases is reported for comparison with previous studies of the age incidence, sex incidence, sites of occurrence, and histologic features. The purpose of this article is to show that there are two types of mucocelcs-one in which mucus has extravasated into the tissues and may or may not be enclosed by granulation tissue (mucous extravasation cyst) and one which is lined with epithelium (mucous retention cyst). The mucous extravasation cyst is the more common type. Included in the eighty cases of mucocele are seven cases in which lesions were diagnosed clinically as ranulas.