Xeroderma Pigmentosum (XP) is a rare, recessive disorder with a more than 1000-fold increase in the frequency of all major skin cancers in association with defective DNA repair. The risk of skin and other cancers among normal appearing XP heterozygote individuals has not been fully studied. We plan to study the family members from XP families with known DNA repair gene mutations to determine if heterozygote carriers of XP disease mutations are at an increased risk of developing cancer. For controls we will compare XP heterozygotes to their non-carrier blood relatives and spouses and to the Surveillance, Epidemiology and End Results (SEER) rates. For this purpose, blood, skin or buccal cells will be obtained from all available relatives for DNA or RNA mutation analysis. Cancer confirmation will be accomplished through review of pathology reports, medical records and death certificates. In addition, willing family members will be clinically examined to determine current cancer status. Individuals who are determined to be heterozygous carriers of XP DNA repair gene disease mutations in these families by mutation analysis or by pedigree will be compared to non-carrier relatives and spouses with respect to history of any type of cancer. We will also focus on skin cancer and cancer of the nervous system since the risks of these cancers are elevated among the XP homozygotes.