The inheritance of sex expression in cucumber (Cucumis sativus) and other cucurbits is well documented; however, the genetics of female sex (gynoecism) expression in bitter gourd (Momordica charantia) has not been described. Inheritance of gynoecism in bitter gourd was studied in a 100% gynoecious line (Gy263B). The F(2) and testcross segregation data revealed that gynoecism in Gy263B is under the control of a single, recessive gene. Following the gene nomenclature of cucurbits, it is proposed that the gene symbol, gy-1, be assigned for the expression of gynoecism in bitter gourd.