Since the application of short duration multidrug therapy (MDT) in leprosy, it has been reported that reversal reactions (RR) may occur after withdrawal of treatment. Surprisingly, such "late reversal reactions" have quite never been described after monosulphonotherapy. Such RR, especially in endemic areas, may represent diagnostic and therapeutic difficult problems. We report 5 cases of late RR. In 4 cases (1 BT patient and 3 BL-LLs patients), the RR occurred 1 month 1/2 to 3 years after cessation of MDT. In the last case (form LLs), the RR happened 6 months after that a 14 years monosulphonotherapy has been stopped. These observations strengthen the need of a complete clinical, bacteriological and immunological evaluation at the time of the diagnostic, more useful than a single bacteriological study, to differentiate late RR from relapses. Moreover, the last case confirms that late RR may occur after monosulphonotherapy.