Accurate diagnosis and assessment of endometriosis by transvaginal ultrasound scan (TVS) can be challenging. We performed an online survey of specialist gynecologists who perform TVS on a regular basis regarding their views as well as clinical experience on the use of TVS in the diagnosis of endometrioma and deep endometriosis (DE). We collected 64 responses. Sixty-one participants (95.31%) answered that they can confidently diagnose endometrioma by TVS "always" or "most of the time". With the exception of DE of the recto-vaginal septum/posterior vaginal vault, for all other DE locations, more than 50% of participants felt that they can "rarely" or "never" diagnose it by TVS in their own clinical practice. Forty-two participants (65.6%) stated that additional, specialized training is required for the diagnosis of endometrioma. When asked about a diagnosis of DE, 58 participants (90.6%) felt that the same is required. The only statistically significant association was between the number of TVSs performed per year and the clinician's ability to diagnose bowel DE in their practice. The answers to all other questions did not differ significantly based on professional status, years of experience post-residency, or number of TVSs per year. Our results demonstrate the delayed adoption of novel diagnostic approaches in endometriosis and confirm the urgent need for specialized ultrasound training.