Data are presented from archaeological excavations conducted by the Institute de Antropología e Historia (IDEAH) in the Mundo Perdido architectural complex, Tikal, Guatemala, from 1979 to 1984. After a brief summary of the data pertaining to the Middle Preclassic, Late Preclassic, and Early Classic periods, new results are presented from investigations of the Late Classic occupation of this group. Many marked social changes at Tikal are revealed through the Mundo Perdido data within a cultural context that emphasizes remarkable continuity.