The southern patas monkey Erythrocebus patas baumstarki is a subspecies thought to be endemic to central north Tanzania but its distribution and abundance is not well documented. We therefore review what is known about the historical and current distribution of the southern patas. It appears that, at present, the southern patas occurs in three populations, in the Serengeti, Mt Kilimanjaro and Arusha. Since 1995 the gaps among these three populations have become larger, thereby increasing their isolation. The available data suggest that, at present, southern patas occur over c. 20,700 km2 (c. 2.3% of Tanzania's land surface area). In 1995 this was c. 30,800 km2 (c. 3.5% of the land surface area). As such, the geographical range of the southern patas has declined by c. 33% since 1995. There are unlikely to be > 900 southern patas today, and there could be < 150. Our recommendations are to (1) maintain an internet accessed database (PatasBase) into which sightings of the southern patas can be entered, (2) interview members of local communities to assess past and current distribution and abundance of the southern patas, (3) conduct field studies to obtain more detailed information on the distribution, abundance, and conservation status of patas in Tanzania, (4) undertake ecological and behavioural research on selected groups of southern patas, and (5) prepare and implement a conservation action plan for the southern patas.