Leprosy is a communicable infectious disease caused by Mycobacterium leprae. Many patients have been infected with M. leprae throughout the years, and until recently the disease was difficult to treat. In the past, lack of efficient drugs resulted in a high cumulative number of leprosy patients. According to the World Health Organization (WHO) the global registered prevalence has fallen dramatically during the last 30 years, and we wanted to look into the reasons for this decline.Methods: Searches performed using PubMed and WHOs websites and library databases.Results: Several events can explain the decline in prevalence: inactivation of cases and release from control, introduction of multidrug therapy (MDT), reduction in treatment length, time of year for the registration of prevalence and alterations of definitions.Conclusions: A consequence of these operational changes has been a fall in prevalence from an estimated 11 million in 1970 to 0.2 million registered cases in 2008. However, leprosy is still a global challenge. Even though estimated prevalence has decreased dramatically from the 1980s, new cases detected (NCD) have remained rather static over the same period of time.