The co-occurrence of autism spectrum disorder and tuberous sclerosis complex has been recognized for decades. The prevalence of tuberous sclerosis complex in the autism spectrum disorder population is 1 to 4%, whereas features of autism spectrum disorder are present in 25 to 50% of individuals with tuberous sclerosis complex. The underlying reason for this association might be a nonspecific disruption of brain function owing to tuberous sclerosis complex, including tuber location, seizures and their effect on brain development, cognitive impairment, a disturbance in brain development in regions associated with autism spectrum disorder, or, less likely, a linkage between a TSC gene and an autism susceptibility gene. Awareness of the relationship between autism spectrum disorder and tuberous sclerosis complex is important during the evaluation of individuals with either disorder. Better delineation of the association and its causative factors is needed for the development of possible interventions.