(1) Background: Uterine rupture during pregnancy is a serious obstetric complication with a high incidence of maternal morbidity and mortality. (2) Methods: The present case is a rare event of a uterine rupture occurring in an unscarred uterus in a nonlaboring primigravida woman in the second trimester. The only risk factor in this case was adenomyosis found in the preconceptional phase. (3) Results: The diagnosis of adenomyosis can often be difficult, so patients should be evaluated by a specialized gynecologist. After careful amnestic collection, a gynecological examination and II level ultrasound should be performed in accordance with the Morphological Uterus Sonographic Assessment classification. (4) Conclusions: This evaluation allows us to identify classes of patients at high risk of uterine rupture who, therefore, must be properly informed of the risks both during preconceptional counseling and during pregnancy.