Thirty-one species of benthic Ostracoda, representing 15 genera and two indeterminate categories, are recorded from water depths greater than 900 m on the continental margin off south-western Africa. Important faunal changes at certain depths allow the assemblages to be grouped into Upper Bathyal, Lower Bathyal and Abyssal zones. The limits of these faunal zones correlate with boundaries within and between the major water masses: the Neritic/Upper Bathyal boundary lies at the bathyal thermocline, which coincides with the base of the salinity minimum zone of the Antarctic Intermediate Water (AAIW) mass (c. 950 m); the Upper/ Lower Bathyal boundary lies at the AAIW/North Atlantic Deep Water (NADW) mass contact (1 500 m); and the Lower Bathyal/Abyssal boundary lies at the top of the NADW core zone (c. 2 000 m). These structural changes in the water column are accompanied by alterations in physical and chemical properties, and we attempt to assess the effectiveness of these as barriers that maintain the integrity of the faunal zones. The relationships are complex and vary greatly from species to species. In addition ,we find that, although the overall abundance of ostracods on the adjacent continental shelf positively correlates with high mud content in the sediments, this relationship does not hold for continental slope and rise area. Certain deep-water species, however, do prefer fine-grained substrates. In comparison with ostracod faunas from similar depths in other parts of the Atlantic Ocean, the populations off south-western Africa have Lower Bathya land Abyssal taxa at somewhat shallower levels. One genus (Rugocythereis) and seven species are new: Krithe capensis, K. spatularis, K .rex, K .peypouqueti, Cytheropteron cronini, Buntonia rosenfeldi, and Echinocythereis whatleyi. Six species have previously been described: Rugocythereis horridus (Whatley and Coles, 1987), Cytherella serratula (Brady, 1880), Dutoitella suhmi (Brady ,1880), Abyssocythere australis Benson, 1971, Poseidonamicus major Benson, 1972, and Henryhowella melobesioides (Brady ,1869). Fourteen species are lef tin open nomenclature.