This species occurs in Viet Nam, Lao PDR and China. In Viet Nam, it occurs west and south of the Black River; it has been extirpated from several areas from which it was previously recorded and is now only known from a few localities in the north-west and north-central parts of this country (Geissmann et al. 2000). In Lao PDR, it occurs in the northern parts, east of the Mekong River, except for a small area in northwestern Lao PDR on the east bank of the Mekong at about 20°17??20°25?N, where it was replaced by N. concolor (Geissmann et al. 2000). In the 1980s, a very small population still occurred in Xishuangbanna in southernmost Yunnan province, China, just across the border from Viet Nam (Hu et al. 1989, 1990), but the species might no longer survive there (W. Bleisch pers. comm. 2006). It was formerly sympatric with N. concolor in Luchin, Yunnan (China), and possibly also in the Ma River region in Viet Nam (Dao Van Tien 1983; Ma and Wang 1988; Geissmann et al. 2000). There may be an apparent overlap or interdigitation between the ranges of N. leucogenys and N. siki between about 19 and 20°N (Groves 2001).