This survey was undertaken in the Errachidia province in south-eastern Morocco in order to inventory the main medicinal plants used in folk medicine to treat arterial hypertension and diabetes mellitus. Four hundred individuals who knew about and/or had used the medicinal plants for the indicated diseases, including some herbal healers, were interviewed throughout different regions of the province. The inventory of medicinal plants is summarized in a synoptic table, which contains the scientific, vernacular and common name of the plant, its ecological distribution, the part of the plant and the preparation used and the therapeutic indication. Extensive investigations have brought to light 64 medicinal plants belonging to 33 families; of these, 45 are used for diabetes, 36 for hypertension, and 18 for both diseases. Of these plants, 34% grow in the wild, 44% are cultivated, and 22% are not indigenous to the area and are brought from other parts of Morocco or from outside the country. The survey shows that 78% of the patients regularly use these medicinal plants. In this region, the most frequently used plants to treat diabetes include Ajuga iva, Allium cepa, Artemisia herba-alba, Carum carvi, Lepidium sativum, Nigella sativa, Olea europaea, Peganum harmala, Phoenix dactylifera, Rosmarinus officinalis, and Zygophyllum gaetulum, and those to treat hypertension include Ajuga iva, Allium cepa, Allium sativum, Artemisia herba-alba Asso, Carum carvi, Nigella sativa, Olea europea, Rosmarinus officinalis, Origanum majorana, Peganum harmala, and Phoenix dactylifera. The local people recognize the toxic plants and are very careful in using such plants, which are Citrullus colocynthis, Datura stramonium, Nerium oleander, Nigella sativa, Peganum harmala and Zygophyllum gaetulum. Our survey shows that traditional medicine in the south-eastern Moroccan population has not only survived but has thrived in the transcultural environment and intermixture of many ethnic traditions and beliefs.