Planktonic foraminifers were examined in at least three samples per core at Site 999 in the western Caribbean Sea (12 degrees 45'N, 78 degrees 44'W; 2829 m water depth) through sediments representing the last approximately 18 m.y. An age model for Hole 999A was constructed using the available magnetic reversal record (down to the top of the Gilbert Chron, 3.58 Ma) and selected planktonic foraminifer datum ages. Near 10 Ma an interval of extremely slow accumulation (5 m/m.y.) corresponds to the "carbonate crash" detected in other Leg 165 studies. Planktonic foraminifer datum ages, as calculated with the Hole 999A age model, are compared to the astrochronological ages assigned to datums at Ceara Rise (Leg 154) and to other published ages. Although there is general agreement, some significant differences are found that may be attributed to either regional paleoceanographic conditions or to shortcomings of the age model for this site. In the middle Miocene temperate latitude globoconellids (Globoconella praescitula, Gc. panda, and Gc. miozea) and in the upper Miocene Neogloboquadrina pachyderma (s) are found regularly at Site 999, suggesting the existence of an influx of cool Pacific surface water and/or regional seasonal upwelling before the emergence of the Central American Isthmus. Menardellid species (Menardella miocenica, M. pertenuis, and M. exilis) endemic to the tropical Atlantic are all encountered at this Caribbean site, although not as regularly or in as large numbers as they were found in the western tropical Atlantic (Leg 154). Several species that were absent from the tropical Atlantic for much of the Pliocene were also found to be missing from the Caribbean record during similar intervals.