O'Donnabhain v. Commissioner 134 T.C. No. 4 is a case decided by the United States Tax Court. The issue for the court was whether a taxpayer who has been diagnosed with gender identity disorder can deduct sex reassignment surgery costs as necessary medical expenses under 26 U.S.C. § 213. The IRS argued that such surgery is cosmetic and not medically necessary. On Feb 2, 2010 the court ruled that O'Donnabhain should be allowed to deduct the costs of her treatment for gender-identity disorder, including sex-reassignment surgery and hormone treatments. In its decision, the court found the IRS position was "at best a superficial characterization of the circumstances" that is "thoroughly rebutted by the medical evidence".