The goal of this study is to propose a new Measure of Internalized Sexual Stigma for Lesbians and Gay Men (MISS-LG) that assesses three dimensions of internalized homonegativity: identity, social discomfort, and sexuality. A convenience sample of 735 Italian lesbians and gay male participants was used to demonstrate the psychometric validity of the scale. Results of confirmatory factor analysis supported three identifiable factors reflecting theoretically based constructs of the MISS-LG. The correlations with other instruments demonstrate the convergent validity: lesbian and gay participants with high internalized sexual stigma describe lower levels of self-disclosure and wellbeing. Implications for research and practice are discussed.