Young adulthood is a difficult period - individuals begin to separate from their families and transition into adulthood, focusing more on themselves and the future. This study aimed to better understand psychosocial and individual differences that contribute to different well-beings for young adults that have siblings without (n=156) and with (target sibling) (n=121) mental illness. Target siblings reported more depressive symptoms and less positive influence of siblings on life decisions. Closeness was related to well-being, but did not interact with sibling type to influence well-being. Both sibling types reported little support and unsupport, and did not differ in coping. Target siblings reported little sibling influence on life decisions at lower levels of perfectionism, but a strong impact at higher levels. This study: confirmed previous findings that sibling types differ in depression; extended findings to include differences in life decisions; and identified factors that did and did not influence well-being.