Stanton v. Stanton, 421 U.S. 7 (1975), is a United States Supreme Court case which struck down Utah's definitions of adulthood as a violation of equal protection: females reached adulthood at 18; males at 21.^{[1]: 217–218}

The case had started in Utah state court.^{[1]: 217–218} A divorced father stopped paying child support for his daughter when she turned eighteen, so the daughter's mother went to court to ask for support until both the daughter and the son reached twenty-one.^[1]: 218 Utah divorce court ruled against the mother, and the Utah Supreme Court held that there was a "reasonable basis" for the differential: women matured earlier and married younger; men had a greater need for education.^[1]: 218 The Utah court stated in its opinion that the basis for the law, though an "old notion," was not unconstitutional.^[1]: 218

Justice Blackmun wrote for the majority.^[1]: 218 He found a violation of equal protection and said the law failed under any standard, including rational basis (the Supreme Court's lowest standard of review).^[1]: 218 The decision remained in the context of child support, without considering different ages for males and females in other contexts.^[1]: 218

The Stanton decision placed the Court on record as declaring that society's stereotypes were not a legitimate basis for official policies that treated men and women differently.^[1]: 218

Blackmun wrote: "A child, male or female, is still a child... No longer is the female destined solely for the home and the rearing of the family, and only the male for the marketplace and the world of ideas... If a specified age of minority is required for the boy in order to assure him parental support while he attains his education and training, so, too, is it for the girl."^[2]

• Gender equality
• List of gender equality lawsuits
• List of United States Supreme Court cases, volume 421