A naturally masculinized female of the Clear Creek gambusia,Gambusia heterochirHubbs, was collected from the headspring of Clear Creek, Menard County, Texas. The fish had 11 well‐developed, late stage embryos. It also possessed an incompletely developed gonopodium and a pair of male‐like, pectoral fins. This discovery constitutes the first report of natural masculinization within the genusGambu