Background: Adenomyosis is a common benign gynecological affecting premenopausal woman, in which there is increased overgrowth of the endometrium with invasion of the underlying myometrium. The precise pathogenesis of adenomyosis remains unknown with many theories being proposed that consider it to be a pathology that initially affects the endomyometrial junctional zone (JZ). Aim of the Work: The study aims to compare 3D transvaginal ultrasound with MRI in diagnosing adenomyosis in comparison with the gold standard histopathology. Patients and Methods: This cross-sectional study was carried out on 77 patients who were recruited from women presenting to the outpatient clinic at Ain Shams University Maternity Hospital planned to undergo hysterectomy (abdominal, vaginal or laparoscopic assisted hysterectomy) for adenomyosis according to the inclusion/ exclusion criteria. Results: Out of 77 patients included in the study, 67(87%) were +ve for adenomyosis by 3D TVUS, confirmed in 46(59.74%) by histopathology, while 52(67.53%) were +ve by MRI, confirmed in 39(50.64%) by histopathology.3D transvaginal US was able to diagnose adenomyosis in 67(87%) patients and fibroid in 23(29.9%) patients, while MRI was able to diagnose adenomyosis in 52(67.5%) and fibroid in 36 (46.8%). Conclusion: our study results indicated that, 3D transvaginal ultrasound is highly accurate as MRI in diagnosing adenomyosis and leiomyoma as a preoperative diagnostic tool. Recommendations: As the 3D ultrasonography is more available, cheaper, less time consuming and easier technique, it is recommended to be used in every day clinical practice, helping the clinicians to reach an accurate diagnosis, select an appropriate treatment, and individualize management for each patient to reach the best outcome therapeutic rates.