This study compares the knowledge of medicinal plants of Bissau-Guinean migrants now established in Italy with the ethnopharmacology still present in their country of origin. We also investigated how traditional ethnobotanical knowledge is changing following the phenomenon of migration from Africa to Europe. The ethnobotanical data were collected during 2017–2018, by interviewing 49 informants belonging to 8 ethnic groups, living in 8 provinces of northern Italy. The final inventory of botanical taxa included 81 species belonging to 34 families, with Fabaceae and Malvaceae the most represented, followed by Euphorbiaceae, Apocynaceae, Combretaceae, and Solanaceae. Plant remedies were used to treat 21 ailment categories, such as fever, internal infections, intestinal and respiratory problems, and pains. The traditional ethnobotanical knowledge of Bissau-Guinean migrants in Italy was associated with gender, with women showing the highest knowledge. In addition, a negative relationship was observed between the maintenance of this knowledge and the number of years migrants have spent in Italy. Overall, a loss of knowledge was observed in the less numerous ethnic groups. However, traditional preparations based on plants from the country of origin are in general well preserved to maintain a good state of health. Our work could help in transferring to the next generation the cultural heritage of Bissau-Guinean people permanently moved to European Countries.