Gender and sexually diverse adolescents have been reported to be at an elevated risk for suicidal thoughts and behaviors. For transgender adolescents, there has been variation in source of ascertainment and how suicidality was measured, including the time-frame (e.g., past 6 months, lifetime). In studies of clinic-referred samples of transgender adolescents, none utilized any type of comparison or control group. The present study examined suicidality in transgender adolescents (M age, 15.99 years) seen at specialty clinics in Toronto, Canada, Amsterdam, the Netherlands, and London, UK (total N = 2771). Suicidality was measured using two items from the Child Behavior Checklist (CBCL) and the Youth Self-Report (YSR). The CBCL/YSR referred and non-referred standardization samples from both the U.S. and the Netherlands were used for comparative purposes. Multiple linear regression analyses showed that there was significant between-clinic variation in suicidality on both the CBCL and the YSR; in addition, suicidality was consistently higher among birth-assigned females and strongly associated with degree of general behavioral and emotional problems. Compared to the U.S. and Dutch CBCL/YSR standardization samples, the relative risk of suicidality was somewhat higher than referred adolescents but substantially higher than non-referred adolescents. The results were discussed in relation to both gender identity specific and more general risk factors for suicidality.