This study identified the most common poisonous and allergenic plants occurring in Sicilian gardens and parks. Based on a survey conducted at 100 sites, a list was drawn up that reports the main biological and toxicological characteristics and ornamental uses of these plants. A total of 137 taxa were recorded, of which 108 were poisonous and 32 were allergenic. The most represented families were the Solanaceae, Moraceae, Apocynaceae and Fabaceae. The most represented geographical contingents were the European and the Mediterranean. A large number of toxic and allergenic plants recorded in Sicilian parks and gardens cause gastrointestinal disorders, 21 of which are deadly poisonous. Based on the results, actions for the management of existing gardens and the construction of new ones are discussed. The importance of environmental education for the population starting from school age is stressed. These recommendations aim to preserve cultivated biodiversity and, at the same time, protect human and pet health.