ImportanceThere has been increasing legislative interest in regulating gender-affirming surgery, in part due to the concern about decisional regret. The regret rate following gender-affirming surgery is thought to be approximately 1%; however, previous studies relied heavily on ad hoc instruments.ObjectiveTo evaluate long-term decisional regret and satisfaction with decision using validated instruments following gender-affirming mastectomy.Design, Setting, and ParticipantsFor this cross-sectional study, a survey of patient-reported outcomes was sent between February 1 and July 31, 2022, to patients who had undergone gender-affirming mastectomy at a US tertiary referral center between January 1, 1990, and February 29, 2020.ExposureDecisional regret and satisfaction with decision to undergo gender-affirming mastectomy.Main Outcomes and MeasuresLong-term patient-reported outcomes, including the Holmes-Rovner Satisfaction With Decision scale, the Decision Regret Scale, and demographic characteristics, were collected. Additional information was collected via medical record review. Descriptive statistics and univariable analysis using Fisher exact and Wilcoxon rank sum tests were performed to compare responders and nonresponders.ResultsA total of 235 patients were deemed eligible for the study, and 139 responded (59.1% response rate). Median age at the time of surgery was 27.1 (IQR, 23.0-33.4) years for responders and 26.4 (IQR, 23.1-32.7) years for nonresponders. Nonresponders (n = 96) had a longer postoperative follow-up period than responders (median follow-up, 4.6 [IQR, 3.1-8.6] vs 3.6 [IQR, 2.7-5.3] years, respectively; P = .002). Nonresponders vs responders also had lower rates of depression (42 [44%] vs 94 [68%]; P < .001) and anxiety (42 [44%] vs 97 [70%]; P < .001). No responders or nonresponders requested or underwent a reversal procedure. The median Satisfaction With Decision Scale score was 5.0 (IQR, 5.0-5.0) on a 5-point scale, with higher scores noting higher satisfaction. The median Decision Regret Scale score was 0.0 (IQR, 0.0-0.0) on a 100-point scale, with lower scores noting lower levels of regret. A univariable regression analysis could not be performed to identify characteristics associated with low satisfaction with decision or high decisional regret due to the lack of variation in these responses.Conclusions and RelevanceIn this cross-sectional survey study, the results of validated survey instruments indicated low rates of decisional regret and high levels of satisfaction with decision following gender-affirming mastectomy. The lack of dissatisfaction and regret impeded the ability to perform a more complex statistical analysis, highlighting the need for condition-specific instruments to assess decisional regret and satisfaction with decision following gender-affirming surgery.