Animal dispersion in space and time results from environmental pressures, and affects the outcome of a species’ social organization. When females are solitary, males may either roam or be pair-living. We studied possible environmental influences affecting the social organization of the round-eared sengi (Macroscelides proboscideus) in a semi-desert in South Africa, using trapping and radio-tracking across 2.5 yr. Adult sex ratios did not deviate from 1:1 and we found no indication of sexual dimorphism in body mass. Females maintained exclusive areas, which had little overlap (<4%) with neighbouring females (NF), and males overlapped predominately only with the home range of single females. Generally, inter- and intra-sexual overlap with neighbouring individuals was low (3–6%) for both sexes, indicating territoriality and pair-living. Pairs were perennial and territories were maintained year-round. However, males generally maintained much larger areas than females, which were sensitive to population density. Male space use appeared to be primarily limited by the presence of neighbouring males. Female home ranges were smaller-sized despite changes in population density, possibly for energetic efficiency. Some paired males attempted to take over widowed females, but shifted back to their original home range following the intrusion of an un-paired male. We conclude that social monogamy is the predominant social organization in round-eared sengis in a semi-desert that may have resulted from females living solitarily in small exclusive territories, balanced sex ratios, and from a low variation of body mass between males.