Growth factors have been implicated in the pathogenesis of autism. We have investigated daily urinary excretion of insulin-like growth factor-1 (IGF-1), epidermal growth factor, and insulin-like growth factor binding protein-3 in autistic children (n = 34, age 2-5 years) and age-matched control children (n = 29). The mean urinary IGF-1 level was lower in the autism group than the control group (p = 0.03). Height was normal. These findings suggest altered IGF-1 metabolism in young autistic children. The cause-effect relationship should be examined by longitudinal studies and insulin-like growth factor provocation tests.