The birth of a child with phenylketonuria (PKU) is almost always a shock to the parents, who are faced with the realities of caring for a child with special needs and the need to cope with the realization that they are obligate carriers of the responsible gene. The Impact of Event Scale (IES) was used to assess the psychological impact of being a PKU gene carrier on 83 parents of children with PKU. IES scores decreased significantly from the time of initial diagnosis of PKU to the current time. The magnitude of the psychological impact did not correlate with the age of the parent, the number of years since the diagnosis of PKU, or the health or development of the child. As more tests become available for detecting the presence of disease-related genes, instruments such as the IES may prove useful in the evaluation of psychological responses to genetic information.