Echinoids are among the most conspicuous and diverse constituents of the Upper Cretaceous and Paleocene marine invertebrate fauna of Argentina. Nine species were collected from localities exposing the Jagüel (Maastrichtian), Roca (Maastrichtian–Danian), Salamanca (Danian), Arroyo Barbudo (Danian), El Fuerte (Danian), and Arroyo Salado (Danian) Formations in northern Patagonia, Argentina. Only one of these taxa, Paraster joannisboehmi (Oppenheim in Böhm, 1903), has been described previously from Argentina. Four taxa, Gauthieria menuthiae (Lambert and Savin in Lambert and Thiéry, 1911), Nucleopygus pullatus (Stoliczka, 1873), Diplodetus nutrix (Lambert in Boule, 1899), and Hemiaster hawkinsi Lambert, 1933, have been described previously from Madagascar. One species, Micropsis desori (Cotteau in Leymerie and Cotteau, 1856), has been described previously from France. One taxon, Pygopistes parrasae is a new species. Argentinian cassiduloids include the only two known Danian species of Nucleopygus and Pygopistes. The spatangoids were not strongly affected by the K-T extinction event. Comparisons of the Patagonian echinoids with those of the Northern Hemisphere indicate that they were strongly influenced by dispersal from Tethyan sources.