Introduction: As breast development in trans women (male sex assigned at birth, female gender identity) who receive gender-affirming hormone treatment is often moderate, they may choose breast augmentation as part of their treatment. Aim: The aim of the study was to investigate the frequency, determinants, and satisfaction of breast augmentation among trans women receiving hormone treatment. Methods: Trans women who started hormone treatment between 1972 and 2018 at our center received an anonymous questionnaire. Main Outcome Measure: The questionnaire contained questions about the start date of hormone treatment, the current age of the respondent, whether or not she underwent breast augmentation, what her considerations in this decision were, and, if the respondent did have breast implants, whether she was satisfied with the result and/or experienced health complaints she attributed to her breast implants. Results: A total of 3,073 questionnaires were distributed, of which 773 were retrieved back (median age of the respondents: 50 years, interquartile range: 35–59). Age and year of start of hormone treatment was comparable between responders and nonresponders. The frequency of breast augmentation varied from 70% in trans women who started hormone treatment between 1980 and 2000 to 20% in those who started between 2010 and 2015. Trans women underwent breast augmentation median 2 years after the start of hormone treatment (interquartile range: 2–4), and 80% was satisfied with the result. Approximately one-third experienced health complaints they attributed to their breast implants. People who considered breast augmentation reported financial limitations as an important reason not to undergo breast augmentation. Clinical Implications: This study shows that it is important to discuss pros and cons of breast augmentation to support trans women in making a well-informed decision. Strengths & Limitations: This is the largest study performed on the frequency and satisfaction of breast augmentation among trans women, which also includes health complaints and considerations in the decision whether or not to undergo breast augmentation. One of the limitations was that we were unable to link other clinical data. Conclusion: 4 of 5 trans women either chose or considered breast augmentation as part of their gender-affirming treatment. Most of the trans women who underwent breast augmentation were satisfied with the result, although approximately one-third experienced health complaints they attributed to their breast implants. Reasons not to undergo breast augmentation included financial limitations. This study shows that it is important to discuss with trans women the positive effects and possible side-effects of breast augmentation to help them make a well-informed decision whether or not to undergo breast augmentation. de Blok CJM, Staphorsius AS, Wiepjes CM, et al. Frequency, Determinants, and Satisfaction of Breast Augmentation in Trans Women Receiving Hormone Treatment. J Sex Med 2019; XX:XXX–XXX.