BACKGROUND tetralogy of Fallot (TOF) is a complex congenital heart disease with clinical and genetic heterogeneity. Of the few known causes, 22q11.2 deletion syndrome (22q11DS) is the most common. We sought to define other clinical subgroups by focusing on cardiac and extracardiac features. METHODS we prospectively screened a cohort of adults with TOF using an established protocol by which subjects were categorized as "syndromic" if they had at least 2 of 3 features: dysmorphic facies, learning difficulties, or voice abnormalities. We then compared the prevalence of cardiac and extracardiac features between subjects in the syndromic group (n = 56) and 112 age- and gender-matched subjects who did not meet our syndromic criteria. RESULTS the syndromic group was more likely than the nonsyndromic group to have pulmonary atresia and/or major aortopulmonary collateral arteries (25% vs 13%, P = .04). There was a trend toward a higher prevalence of one or more major congenital extracardiac anomalies, primarily involving the musculoskeletal and genitourinary systems (25% vs 13%, P = .06). Later-onset conditions, including neuropsychiatric disorders (32% vs 17%, P = .03), thyroid disorders (20% vs 4%, P = .001), and hearing deficits (20% vs 0, P < .001), were more common in the syndromic group. The syndromic group tested (n = 50) had neither 22q11.2 deletions nor karyotypic anomalies. CONCLUSIONS similar to 22q11DS, adults with TOF meeting screening criteria for a possible genetic syndrome are enriched for more severe cardiac disease and late-onset extracardiac features. Increased awareness of this subgroup with a multisystem condition may be helpful for identifying individuals for referral to medical genetics and optimizing management.