Friends are a vital source of social relations throughout the lifespan and across developmental stages. Our knowledge of how friendships develop over time, especially from childhood through adulthood, is limited. Furthermore, it is now recognized that this specific type of relationship influences health across the life course in unique ways. Using the Convoy Model of Social Relations as a guiding framework, this study charts the multiple and unique trajectories of friendship across adulthood and tests whether these trajectories influence health differentially by age. The sample for the study consisted of 553 adults from the longitudinal Social Relations Study. Respondents ranged in age from 13 to 77 at Wave 1 (1992), and included only those who reported a best friend in each wave, that is, Wave 2 (2005) and Wave 3 (2015). Approximately 65% of the respondents were women, and 24.5% were people of color. Latent growth curve analysis identified three trajectories of the presence of friends in one's network over time, two trajectories of positive friend quality, and three for negative quality. The most consistent findings are associated with positive friend relations over time. Gender was associated with friendship quality where women reported more positive friend relations over time, and increasing positive friend relations predicted better health 23 years later. These findings demonstrate that consistent and increasing positive friendships yield health benefits over time, whereas the presence of friends and negative quality does not have an effect. Overall, findings advance understanding of the long-term effects of social relations across the lifespan and life course. (PsycInfo Database Record (c) 2024 APA, all rights reserved).