The results are generally permanent, provided that you maintain your weight following the treatment. Its use to treat cellulite is not-permanent, however, as this can easily reoccur over time.
A European study demonstrated significant circumferential reduction in all 58 trial volunteers after 4-5 treatments. Another study demonstrated longevity of results up to at least 18 months.
The longevity of the results will depend on your genetic predisposition to ageing and your lifestyle; you may need top-up treatments to maintain the results.