This trial aims is to determine the effect of umbilical cord blood infusion in treating children with autism. The trial is being undertaken by the Sutter Institute for Medical Research in Sacramento California and expects to recruit 30 children from 2 to 7 years of age that have been diagnosed with autism. Participants will be randomly divided into two groups. One group will receive an infusion of their own umbilical cord blood (initial experimental group). The other group will receive a placebo infusion of saline, but then after 24 weeks, they will receive their own umbilical cord blood. The initial experimental group will receive a placebo injection at 24 weeks. Both groups will be tested at 24 weeks after initial infusion, and then again after another 24 weeks. The participants, their carers and their doctors will not know which group they have been assigned to. In the follow-up period each child will be monitored for complications and changes in their clinical condition. The trial commenced in August 2012 and is expected to conclude in August 2013.