Change with time in the amount of dolomite in post-Jurassic deep marine sediments was tabulated using 844 Deep Sea Drilling Project samples that contain 5% or more dolomite and could be suitably dated. Superimposed on an overall decrease since Early Cretaceous time are two maxima in the Cretaceous, a maximum at the Paleocene/Eocene transition, and a maximum in the Neogene. Frequency trends in the Atlantic and Indo-Pacific are similar overall but differ in detail. Mediterranean and Red Sea data are Neogene and peak in the mid-Miocene and late Miocene to early Pliocene, respectively. Data from the Gulf-Caribbean are largely Neogene and suggest deepening since early Cenozoic time. The general similarity of the patterns in the Atlantic and Indo-Pacific, supported by data from the smaller basins, suggests that the frequency of occurrence of dolomite in deep marine sediments may be related to a common global cause, possibly the flooding and draining of shallow shelves and small ocean basins consequent upon eustatic sea-level changes.