A long-term Danish study of 454 people compared the rates of mental-health problems in those who had been diagnosed with childhood autism to those free of the condition. The study found that 48.3% of the autistic group had been in contact with psychiatric hospitals over the course of the study compared to just 6% of those without the condition. 17% of the autistic group had been diagnosed with a mental illness compared to 2.7% of the control group. Those who had been diagnosed with autism in childhood were nearly four times as likely to be diagnosed with schizophrenia and nearly three times as likely to suffer from depression.
Mouridsen, Svend Erik ... [et al] - Psychiatric disorders in individuals diagnosed with infantile autism as children: a case control study Journal of Psychiatric Practice January 2008, 14(1), 5-12