A recent sampling endeavour of freshwater crabs along the high-lying streams of the Nyanga mountain range in Mutare (Eastern Highlands, Zimbabwe) yielded a morphologically distinct, as yet undescribed species. The novel Zimbabwean species is compared to the 16 described species from southern Africa based on mtDNA sequence data derived from three partial gene sequences (12S rRNA, 16S rRNA and COI). The new Zimbabwean species was found to be a sister taxon to Potamonautes mulanjeensis. These two species are morphologically and genetically easily differentiated. The new species is described as Potamonautes mutareensis, sp. nov. and is compared morphologically to the known freshwater crab species of southern Africa. A dichotomous key to the four described freshwater crab species that occur in Zimbabwe is also provided. Our results suggest that species diversity and endemism of freshwater decapods and other habitat specialists is likely to be high in unsampled mountainous regions.