Autism spectrum disorders are neurodevelopmental disorders that are thought to be caused by a gene-by-environment interaction and in which various immune alterations are reported. We investigate CD4⁺ T-cell cytokine profiles and subpopulations in 19-year-old monozygotic twins with autism and different comorbidities. CD4⁺ T cells from the twin with epilepsy produce more interferon-gamma, less interleukin-17, and have an increased interferon-/interleukin-4 ratio. CD4⁺ T cells from the twin with multiple sclerosis exhibit a cytokine profile similar to an age and gender-matched control and a higher percentage of T regulatory (T_reg) cells. The twins’ mother’s T cells produce very high levels of both interleukin-17 and interferon-. Cytokine and CD4⁺ T-cell abnormalities in the twins could contribute to or be a result of the manifestation of their divergent comorbidities. A proinflammatory, autoimmune-polarized cytokine profile is observed in this unique family with autism.