The number of lesbian, gay, and bisexual (LGB) adults aged 50 and older is projected to reach 5 million in the U.S. by 2030 (Fredriksen-Goldsen, Kim, Shiu, Goldsen, & Emlet, 2015). Older bisexuals experience more negative mental and physical health outcomes when compared to both heterosexuals and other sexual minorities (Fredriksen-Goldsen, Shiu, Bryan, Goldsen, & Kim, 2017). As bisexuals are the numeric majority of sexual minorities in the U.S. (Herbenick et al., 2010), bisexual aging processes are critical to understand if researchers wish to reduce sexual minority health disparities and promote healthy aging. In the current study, we use a national probability sample of adults from the Midlife in the United States (MIDUS) study to assess life satisfaction across an 18-year period. We aimed to identify whether life satisfaction-an indicator of psychological health and well-being-is similar for same-age bisexual, lesbian and gay, and heterosexual midlife individuals, and whether sexual orientation predicts change in life satisfaction across adulthood. Further, we tested whether life satisfaction among bisexuals changes at the same rate and in the same pattern as for lesbian, gay, and heterosexual individuals. Overall, we found a linear pattern of increase in life satisfaction across adulthood. However, when we accounted for sexual orientation, a different pattern emerged for bisexuals. Whereas heterosexuals and lesbian and gay individuals experienced increases in life satisfaction across adulthood, bisexuals' life satisfaction did not increase over this period. Implications for bisexual health and well-being are discussed.