Latitudinal gradients of species diversity are ubiquitous features of terrestrial and coastal marine biotas, and they have inspired the development of theoretical ecology. Since the discovery of high species diversity in the deep-sea benthos, much has been learned about local and regional patterns of diversity. Variation in diversity on larger scales remains poorly described. Latitudinal gradients of diversity were unexpected because it was assumed that the environmental gradients that cause large-scale patterns in surface environments could not affect communities living at great depths. Here we report that deep-sea bivalves, gastropods and isopods show clear latitudinal diversity gradients in the North Atlantic, and strong interregional variation in the South Atlantic. Many seemingly incompatible mechanisms have been proposed to explain deep-sea species diversity. The existence of regular global patterns suggests that these mechanisms operate at different spatial and temporal scales.