Knowledge about prevalence rates of psychiatric disorders and mental health services use among parents and relatives of persons with autism spectrum disorder (ASD) is limited, particularly when referring to epidemiologic samples. The current study is based on an island-wide probabilistic multistage cluster sample of adult individuals (N = 3062) living in Puerto Rico. Results showed a significantly higher rate of attention deficit hyperactivity disorder and serious mental illness in parents (n = 34) or relatives (n = 34) of ASD individuals, as compared with the Puerto Rico adult population as a whole. Although not definitive because of the small sample size, the fact that the rates of mental health utilization were similar to the population sample suggests a need for greater attention by health professionals attending children with ASD to the needs for mental health services of both parents and relatives of individuals with ASD.