Increasing evidence suggests that immunological factors are involved in the pathogenesis of autism spectrum disorders (ASD). The present study examined whether immunological abnormalities are associated with cognitive deficits in children with ASD. Eighteen high-functioning (HFA) and 19 low-functioning (LFA) children with ASD, aged 8-17 years, were assessed on cognitive functioning using IQ tests and executive functions tests including the Five Point test, Children Color Trail-making Test, D2 Test of Concentration, Tower of California Test; Hong Kong List Learning Test, and Go/No-Go test. They were also assessed on autoimmune symptoms, reported by their parents; and immunological measures including T lymphocytes (CD3+), B lymphocytes (CD19+), T helper lymphocytes (CD3+CD4+), suppressor/cytotoxic T lymphocytes (CD3+CD8+), and natural killer (NK) cells (CD3-CD16+ and/or CD56+). LFA children showed greater deficits in executive functions as well as higher levels of total lymphocyte, T lymphocyte and suppressor/cytotoxic T lymphocyte levels than HFA children (all p less than 0.05). Their executive functions were also significantly associated with the three lymphocyte levels (all p less than 0.05). These findings support the notion that altered immune functions may act on the neural tissues of individuals with ASD, which in turn leads to their cognitive dysfunctions. (Contains 4 tables.)