Objective: This descriptive study aimed to assess the prevalence and characteristics of pelvic pain and explore predictive factors for pelvic pain in transgender (trans) individuals using testosterone therapy. Design: Cross-sectional survey. Setting: Online. Sample: Trans people presumed female at birth, using testosterone for gender-affirmation, living in Australia, and aged > 16 years. Methods: Logistic regression was applied to estimate the effect size of the possible factors contributing to pain after starting testosterone. Main Outcome Measures: Prevalence and characteristics of pelvic pain following initiation of testosterone therapy, type and length of testosterone therapy, menstruation history, and relevant sexual health, gynaecological and mental health experiences. Results: Among 486 participants (median age 27 years), 351 (72.4%) reported experiencing pelvic pain following initiation of testosterone therapy, described most commonly as in the suprapubic region and as “cramping”. Median duration of testosterone therapy was 32 months. Persistent menstruation, current or previous history of post-traumatic stress disorder, and experiences of pain with orgasm were associated with higher odds of pelvic pain after testosterone therapy. No associations were observed with genital dryness, intrauterine device use, previous pregnancy, penetrative sexual activities, touching external genitalia, or known diagnoses of endometriosis, vulvodynia, vaginismus, depression, anxiety, or obesity. Conclusions: Pelvic pain is common in trans people following initiation of testosterone therapy. Given the association with persistent menstruation and orgasm, as well as the known androgen-sensitivity of the pelvic floor musculature, further research into pelvic floor muscle dysfunction as a contributor is warranted.