Abstract Cowden's syndrome or multiple hamartoma and neoplasia syndrome is a hereditary disorder combining multiple hamartomas of many organs. These hamartomas are derived from ectodermal, mesodermal, and endodermal tissues and may undergo spontaneous malignant changes. Small papular cutaneous lesions and papillomatous outgrowth and papular lesions of the oral mucosa are the most predominant features of the syndrome. Since the orocutaneous lesions often precede the associated malignant degenerations, they may serve as a diagnostic signal for the probably developing neoplasia in other organs. The presence of extensive papillomatous and papular lesions in the oral mucosa combined with skin lesions should therefore alert the clinician to suspect the presence of Cowden's syndrome, the early diagnosis of which is important in order that the concomitant malignant changes might be discovered at the earliest possible moment. Four cases of Cowden's disease are presented, with emphasis on the oral manifestations of this syndrome.