We investigate mitochondrial DNA and craniometric variation in southern African and Malagasy populations of the small and morphologically variable, house-roosting molossid bat, Chaerephon pumilus in relation to Malagasy populations of the related, smaller-sized species, C. leucogaster. Both cytochrome b and D-loop sequences show C. leucogaster to be nested within C. pumilus sensu lato, with Malagasy C. pumilus forming a sister group to African C. pumilus and Malagasy C. leucogaster. Four distinct D-loop clades are found in southern African populations, all of which occur sympatrically in the greater Durban area of KwaZulu-Natal Province, whilst two of the Durban clades also characterize 1) northern KwaZulu-Natal and low-lying (<600 m) areas of Swaziland, and 2) ‘inland’ populations comprising the Kruger National Park and higher-lying (>600 m) areas of Swaziland. Clades from low-lying areas show evidence of historical demographic expansion around 3300–13 000 years ago (KwaZulu-Natal coastal clade, Clade A1) to 14 700–60 000 years ago (Durban clade, – Clade B1), whilst the inland clade (Clade B2a) was demographically more stable. The origin of these clades can be explained by sea level and vegetation changes hypothesized to follow the Last Glacial Maximum (LGM) after 18 000 years ago. Sympatric clades are shown to differ significantly in the proportional width of the braincase, and ongoing work will test evidence for acoustic and other morphological differences between them.