Despite an age-old tradition of olive growing and its geographical location, Iran was apparently free of the olive fly, Bactrocera oleae (Rossi, 1790) (Diptera: Tephritidae), the major worldwide olive tree pest, until the last decade. However, this situation has changed radically since B. oleae was first reported in 2004, and the olive fly is now Iran's most important pest of olive trees, and a very serious threat to olive production in the Northern and more humid parts of the country. Genetic analyses of mitochondrial markers of B. oleae collected in the traditional olive growing area in Northwestern Iran were used to determine the origin of this pest. The results indicate it was most likely imported on olive trees from the Central Mediterranean area.