To address the natural history of Williams syndrome (WS), we performed multisystem assessments on 20 adults with WS over 30 years of age and documented a high frequency of problems in multiple organ systems. The most striking and consistent findings were: abnormal body habitus; mild–moderate high frequency sensorineural hearing loss; cardiovascular disease and hypertension; gastrointestinal symptoms including diverticular disease; diabetes and abnormal glucose tolerance on standard oral glucose tolerance testing; subclinical hypothyroidism; decreased bone mineral density on DEXA scanning; and a high frequency of psychiatric symptoms, most notably anxiety, often requiring multimodal therapy. Review of brain MRI scans did not demonstrate consistent pathology. The adults in our cohort were not living independently and the vast majority were not competitively employed. Our preliminary findings raise concern about the occurrence of mild accelerated aging, which may additionally complicate the long-term natural history of older adults with WS. We provide monitoring guidelines to assist in the comprehensive care of adults with WS. © 2004 Wiley-Liss, Inc.