Feline xanthinuria is a rare disease that results in excessive urinary output of xanthine, a substance insoluble in water. Often, this leads to xanthine crystallization and urinary tract obstruction. It is caused by a mutation in either the xanthine dehydrogenase (XDH) gene or the molybdenum cofactor sulfurase (MOCOS) gene. The XDH gene was studied to identify the location of the mutation in a hospitalized cat exhibiting the disease. Primers were designed for the 36 exons of the XDH gene, and each was given a temperature gradient PCR, then used in a PCR to amplify DNA for gel extraction. The resulting DNA was sequenced to compare to the published cat genome. Exons 1-4,7-15,17-20,25, and 31-36 were successfully sequenced. The location of exon 22-23 was identified as a possible site for the mutation as a temperature gradient using the affected cat’s DNA and the exon 22-23 primer produced no DNA band in a gel, indicating a mutation causing the primers to malfunction. However, further sequencing needs to be completed to confirm this theory.