The prevention and treatment of mental health concerns are consistently named among autistic adults' highest clinical and research priorities. While several theories have been proposed to explain the high prevalence of depression and anxiety in autistic populations, virtually no longitudinal research has evaluated causal mechanisms. The first study in this dissertation aims to explore how known contributors to depression and anxiety identified by general population research -- namely, rumination, dissatisfaction with social connectedness, and distressing sexual experiences -- relate to the development of internalizing symptoms in autistic individuals during the transition to college. The second study explores potential contributors to sexual risk, through investigating differences in sexual consent understanding and experiences in autistic and non-autistic undergraduates. Results suggest that hypothesized predictors tend to primarily contribute to depression and anxiety symptoms during the transition to college through a) a baseline tendency that seems to have some persisting, longer-term influence throughout the semester and b) a synchronous, short-term risk that may contribute to symptoms in the moment. Findings also support prior literature that autistic adults endorse more childhood experiences of sexual abuse and unsatisfying sexual education experiences. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]