Gene therapy for the treatment of disease in children and adults is being actively pursued at many medical centers. However, a number of genetic disorders result in irreversible damage to the fetus before birth. In these cases, as well as for those with genetic diseases who may benefit from therapy before symptoms are manifested, in utero gene therapy (IUGT) could be beneficial. Although some successes with in utero gene transfer have been reported in animals, significant questions remain to be answered before IUGT clinical trials would be acceptable. This review analyzes the state of the art and delineates the studies that still need to be performed before it would be appropriate to consider human IUGT.