The present study examined patterns of serious mental illness (SMI), specific mental health syndromes, and service use among older (65ϩ) and younger (18 -64) adults throughout the United States, and the extent to which various factors predict SMI and the use and magnitude of mental health treatment. Despite recent developments designed to improve mental healthcare access and treatment for older adults, older individuals were found to receive outpatient mental healthcare at very low rates. Compared to younger adults, older adults were three times less likely to report receiving treatment. Although prevalence estimates for SMI and specific syndromes were markedly lower among older than younger adults, older individuals most in need of care were highly unlikely to report receiving treatment. Findings point to the importance of perceived need in mental healthcare use. Significantly, however, those older adults that made it into services typically reported benefiting considerably from treatment, at least as much as all other age groups. Several predisposing, enabling, and need factors related to mental illness and service use were identified that have important implications for how we plan for, design, and deliver mental health services to older and younger Americans.