Objectives: Prenatal and birth history as potential sources of risk factors in relation to the onset of autism were examined. Methods: A cohort of 164 families of autistic children referred to The Autism Center at New Jersey Medical School—UMDNJ, Newark, New Jersey, over a two-year period was studied. Intake prenatal and birth history information was obtained from each family and reviewed by a clinician. Results: Prevalence rates in this cohort for vaginal bleeding, prolonged labor and prematurity were higher than comparable rates reported nationally and in New Jersey. Clustering of multiple prenatal risk factors was observed. This clustering was associated with the age of the mother, but uncorrelated with birth order. Conclusions: These findings support the general hypothesis that systemic problems at the prenatal stage may form a distinct dimension of risk associated with autism.