Anomalously shallow regions in the form of bathymetric swells are a common occurrence in ocean basins. The elevation of these swells could originate from pressure forces at the base of the lithosphere caused by mantle convection, compositional changes leading to increased buoyancy of the lithosphere, or thermal expansion caused by reheating of the lithosphere. The third explanation, thermal rejuvenation, must be an important factor in the formation and evolution of bathymetric swells in every test we applied, we found midplate swells to behave like oceanic crust reset to a younger thermal age. From the subsidence of atolls and guyots on lithospheric swells, it appears that they sink along the thermal cooling curve for normal oceanic crust of the same depth but younger age as defined by magnetic isochrons. The distribution of volcanoes in the oceans suggests that older crust acts as a thermal barrier to midplate vulcanism. If swells are thermally rejuvenated, therefore, they should be more likely spots for volcanism. As predicted swells commonly show overprinting of several distinct hot spot traces and remain extremely favorably sites for midplate vulcanism even when the direction of plate motion changes. Flexural rigidity values obtained from islands and seamounts superimposed on swells place constraints on the form of the thermal rejuvenation process. For the Hawaiian swell, the fact that the effective elastic-plate thickness is much larger than would be expected from younger litosphere at the same depth requires that the heating be confined to the lower lithosphere only. In the case of Great Meteor Guyot, the initial swell depth and elastic-plate thickness are both appropriate for lithosphere with an equivalent thermal age of 20 m.y. At least in this case, reheating of the entire lithospheric column remains a possibility. Lithosphere subjected to several reheating events, such as in the Cook-Austral and Society Islands area, is particularly likely to display a significant reduction in the elastic-plate thickness.