The ancient, but only recently discovered, Maya site of Pacbitun, located in the Cayo District of western Belize, is a compact, medium-sized lowland center first settled about 900 B.C., during the Middle Preclassic Period. The settlement expanded in succeeding centuries, and flourished during the Late and Terminal Classic Periods (A.C. 550--900) before being abandoned. Field investigations during 1986 and 1987 have resulted in a detailed map of the ruins, which have an acropolis center nearly 0.5 sq km in area and incorporate 5 plazas and 41 major structures. These include residential, range-type buildings, organized into courtyard quadrangles; temple-pyramids with remains of vaulted superstructures; a pair of lengthy causeways; and a ceremonial ballcourt. In this preliminary report summaries of the architectural excavations as well as brief descriptions of the monuments, burials, caches, and artifacts are provided.