This paper reports an ethnobotanical study conducted in the year 2000 in the Natural Park of "Serra de São Mamede" (Portugal). Informal interviews involving 45 informants provided data about 165 useful plants, 150 of which had medicinal and/or aromatic use. Two hundred and twenty-four popular names were noted, 98 of which had not been documented before. The most relevant plants are mentioned in this paper, along with their local names, the parts of them used, popular uses (or troubles treated), preparation and administration processes, and citation frequency. This is the first study of medicinal and aromatic plants in Portugal to use ethnobotanical methodology.