Leprosy today is a problem of global magnitude affecting possibly up to 15 million people. Its rise and fall in medieval Europe is an historically fascinating enigma. Partial cross-immunization by epidemic tuberculosis, reinforced by the growth of cities, has been proposed as a mechanism in leprosy's European disappearance, but evidence is lacking. In the case of Africa in recent decades, analysis of leprosy and tuberculosis rates, and of levels of urbanization, albeit with imperfect data, suggests a possible environmental hearth for leprosy, the existence of some cross-interference between tuberculosis and the milder, paucibacillary form of leprosy, and a negative correlation between leprosy and urbanization. It is argued that the rise of the city in Africa, acting through a combination of influences, including tuberculosis, is leading to a decline of leprosy.