Autism spectrum conditions (henceforth autism) are a set of lifelong, neurodevelopmental conditions characterized by social and communication difficulties; markedly restricted, repetitive interests and behavior; and differences in cognitive profile including atypical sensory perception and information processing, motor abilities, and intellectual ability. Existing evidence suggests that autistic individuals may be at higher risk of premature mortality, and that increased likelihood of comorbid physical health conditions may be contributing to this risk; however, most of the existing research focuses heavily on the experiences of young adults. This thesis aims to broadly describe the experience of autistic individuals across the adult lifespan, including the areas of chronic disease comorbidity, lifestyle behaviors, identity, and healthcare. In Chapter 1, I discuss the challenges that autistic individuals (and particularly adults and females) currently face, and how these areas can affect both length and quality of life. Chapter 2 provides an outline of all the methodologies utilized throughout the thesis. Chapters 3-6 utilize data from the Autism and Physical Health Survey to compare the experiences of autistic and non-autistic adults regarding risks of cancers, cardiovascular conditions, respiratory conditions, and diabetic conditions (Chapter 3); diet, exercise, and sleep, as well as their relationships to body mass index (BMI) and chronic disease risk (Chapter 4); sexual health and sexual orientation (Chapter 5); and smoking, alcohol use, and recreational drug use (Chapter 6). Chapter 3 confirms previous findings in samples of primarily younger adults to suggest that autistic individuals across the adult lifespan have greater risks of cardiovascular, respiratory, and diabetic conditions (which persist even after accounting for BMI, smoking, and alcohol use), and that these risks may vary based on biological sex. Chapter 4 provides the results of the first study to broadly describe the diet, exercise, and sleep patterns of autistic adults, and the first to consider their relationships to BMI, cardiovascular and health outcomes. The findings suggest that autistic individuals (and particularly autistic females) are more likely to exhibit unhealthy patterns, including restricted diets, insufficient nutrition, limited exercise, diminished sleep duration, and sleep disturbances; there is also some preliminary evidence that these patterns may relate to risk of cardiovascular conditions. Chapter 5 suggests that autistic individuals are far more likely to identify as asexual or ‘other’ sexual orientations (and less likely to identify as heterosexual); less likely to have ever engaged in sexual activity; and that they are equally likely as non-autistic individuals to contract sexually transmitted infections (STIs). In Chapter 6, I employ a mixed methods approach to illustrate that, despite relatively limited quantitative differences in frequency of substance use, autistic individuals are far more likely to report qualitative differences in motivations for using or abstaining from substances alongside vulnerability associated with substance use. In Chapters 7 and 8, I investigate the risk of cancer overall, as well as for hormone-associated cancers among autistic individuals and non-autistic mothers of autistic individuals (NMAI), respectively. These studies use large samples of General Practitioner (GP) records, provided by the Clinical Practice Research Datalink (CPRD), as well as cancer records from the National Cancer Registry and Analysis Service (NCRAS) from Public Health England (PHE). Chapter 9 utilizes the Autism and Healthcare Experiences Survey to identify differences in the healthcare experiences of autistic and non-autistic individuals in the areas of access and advocacy, sensory processing, communication, stress, system problems, and shutdowns and meltdowns. Finally, in Chapter 10, I summarize and integrate the empirical findings across Chapters 3-9. I discuss their implications for understanding of the experience of autistic adults facing increased risk of chronic health conditions and limited support. I also discuss the strengths and limitations of each of the studies, future directions of research, and implications for healthcare providers working with autistic patients.