Autistic postsecondary students reportedly experience significant social anxiety and loneliness, which has become a growing concern for colleges and practitioners alike. The social-emotional experiences of autistic students entering postsecondary education in science, technology, engineering and mathematics (STEM) at 4-year institutions are not well understood. This study examined the degree to which autistic postsecondary STEM students experience loneliness and social anxiety, and explored how these aspects of social-emotional functioning are related to autism severity and adjustment to college. Data were from online surveys completed by STEM college students enrolled in an autism support program at a 4-year technology school (N = 78), who were also receiving support in the form of coaching. Surveys were distributed at two points in time, which resulted in cross-sectional data for two groups and repeated measures data for a smaller group. There were few significant differences between the cohorts' levels of loneliness and social anxiety, with over two-thirds of both samples reporting elevated loneliness and social anxiety. A large proportion (40%) of both cohorts met criteria for social anxiety disorder (SAD). More severe autism traits were associated with higher loneliness and social anxiety, and there was a compelling relationship between more severe autism traits and increased social anxiety. The repeated measures group did not show differences in loneliness or social anxiety from Time 1 to Time 2, suggesting that autistic students may experience social-emotional difficulties either chronically or at various times during college. Implications are discussed for postsecondary autism support programs, particularly regarding monitoring and intervention for reducing loneliness. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]