This study reports stable carbon-isotope ratios for both bone collagen and apatite, and nitrogen-isotope ratios for bone collagen for 72 Maya skeletons from 9 zones representing contrasting status groups at Altun Ha, Belize. The sample spans the Preclassic to Postclassic periods, approximately 800 B. C. to after A. D. 950. Although Altun Ha has a maize-based (C-4) diet, it has a much stronger marine/reef component than any other Maya site studied so far. Two possible dedicatory burial groups are dietarily distinct. The source of protein appears to have been fairly stable throughout the site sequence, but a marked shift to reduced consumption of C4 foods seems to have occurred after the Early Classic period. A second similar decline probably occurred between the Late/Terminal Classic and the Postclassic periods. These apparent temporal trends may, however, be confounded by differences between zones. High status is marked by consumption of large quantities of C4 foods, possibly including C4-fed terrestrial animals. Males consumed more meat and C4 foods than did females. All δ-values and collagen-apatite spacings indicate that children were breastfed until at least the age of three or four.