Social interactions where a person is addressed by their correct name and pronouns, consistent with their gender identity, are widely recognized as a basic and yet critical aspect of gender affirmation for transgender people. Informed by the Model of Gender Affirmation, we developed a self-report measure of the importance of social gender affirmation, the Transgender Women's Importance of Pronouns (TW-IP) scale, which measures gender affirmation through the usage of correct pronoun by others. Data were from self-administered surveys in two independent samples of transgender women living with HIV in the US (N1 = 278; N2 = 369). Using exploratory factor analysis with data from Study 1 and confirmatory factor analysis with data from Study 2, we obtained a four-item scale with a single-factor structure and strong reliability (α = 0.95). We present evidence of TW-IP's convergent and discriminant validity through its correlations with select mental health and HIV-related measures. Further, scores on TW-IP were linked in expected directions to several hypothesized mental health and HIV care outcomes, demonstrating its predictive validity. The resulting brief measure of importance of pronouns among transgender women shows strong psychometric properties. Validation evidence offers highly promising opportunities for use of the measure in clinical and research settings.