Individuals diagnosed with autism spectrum disorder (ASD) have a higher probability of developing co-occurring mental or physical health conditions. However, little is known about how these health conditions develop and impact the lives of the adult ASD population. This paper reviewed existing studies concerning factors affecting the health status of adults with ASD and described their outcomes and prevalence. A systematic search of electronic databases yielded 21 studies eligible to be included. The most common physical problems affecting health were epilepsy and immune, gastrointestinal, and sleep disorders. Mental health disorders, most prominently mood and anxiety disorders and OCD, were also strong factors for determining health in adults. Future research should focus on measuring the overall health status of the adult ASD population.