Background: Transgender women (people assigned male genders at birth with female gender identities) can choose to cryopreserve semen before their medical transition, to retain the possibility to parent genetically related offspring later in life. Our previous retrospective study showed that semen quality in transgender women was decreased compared with the general population. The etiology of this impaired semen quality remains largely unknown. However, impaired semen quality might be related to habitual behavior more typically observed in transgender women, for example, the desire to hide their testicles because of genital dysphoria. Therefore, we decided to conduct a consecutive study with prospectively obtained data on behavior and lifestyle in transgender women. Objective: This study aimed to study the influence of a low ejaculation frequency, wearing tight undergarments, and bringing the testes in the inguinal position (tucking) on semen quality in transgender women at the time of fertility preservation. Study Design: In this cohort study, transgender women were included between May 2018 and September 2020, at the time of fertility counseling, before the start of hormonal treatment. Data were collected on demographics, lifestyle factors, medical history, endocrine laboratory results, and semen parameters. Semen parameters were categorized using reference values for human semen of the World Health Organization and compared with semen quality in the general population. The odds ratios with 95% confidence intervals were calculated using multivariable logistic regression analysis to assess the impact of tucking, wearing tight undergarments, and a low ejaculation frequency on semen quality, correcting for potential confounders. Results: Overall, 113 transgender women were included. Median semen parameters were significantly decreased than the general population. Crude logistic regression analyses showed an association between always wearing tight undergarments (odds ratio, 3.06; 95% confidence interval, 1.11–8.49) and extensive tucking (odds ratio, 6.09; 95% confidence interval, 1.54–24.01) on having a total motile sperm count of <5 million. Multivariable analyses showed that the association with tucking was independent of demographic factors, lifestyle factors, and medical history (odds ratio, 7.95; 95% confidence interval, 1.66–37.99). However, this was not the case for the association with always wearing tight undergarments (odds ratio, 2.89; 95% confidence interval, 0.95–8.82). Ejaculation frequency did not influence total motile sperm count. Conclusion: Behavioral factors, including wearing tight undergarments and extensive tucking, may contribute to the lower semen quality in transgender women. These results will enable optimization of fertility counseling on how to adjust lifestyle before pursuing semen cryopreservation.