Endometriosis is a common and often debilitating gynaecological disorder that affects 5-10% of women. The prevalence is even higher among women with symptoms of endometriosis which include chronic pelvic pain, acquired dysmenorrhoea, dyspareunia, dyschezia, menorrhagia, abnormal bleeding and infertility. Approximately 80% of women suffering from endometriosis will develop superficial lesions while 20% will develop deep infiltrating endometriosis (DIE). The removal of deep infiltrating endometriosis is significantly more complex, particularly when pouch of Douglas obliteration or bowel nodules are present. The surgery can usually not be completed unless DIE was diagnosed preoperatively. The technique to diagnose deep infiltrating endometriosis with transvaginal ultrasound (TVUS) was first described in detail in 2009. Since then, the accuracy of TVUS for the prediction of DIE has been well established in the literature. Transvaginal ultrasound is widely used as a first line of investigation for women with gynaecological symptoms. Because endometriosis is a very common cause of gynaecological symptoms in women of the reproductive age group, including the assessment for DIE in the routine pelvic ultrasound allows earlier diagnosis and better surgical outcomes for all women with deep infiltrating endometriosis. This presentation describes in detail the different steps required to obtain a transvaginal ultrasound diagnosis of deep infiltrating endometriosis.