Disorders of sex development (DSD) are a group of congenital conditions presenting with differences in the chromosomal, gonadal, or anatomic sex development. Evaluating the chromosomes, gonads, and internal and external genitalia of the patients is important for understanding DSD. Furthermore, confirming the presence of a uterus is essential for the assessment of the internal genitalia status. Although the uterus can be identified by ultrasonography, magnetic resonance imaging, or laparoscopy, it may be easily overlooked. Here, we report the case of a patient with mixed gonadal dysgenesis, in whom the presence of a uterus could not be confirmed before the initiation of estrogen replacement therapy despite the performance of various tests. The detection of the uterus was prompted by an atypical genital bleeding. This case implies that physicians may have difficulties identifying the uterus in female patients with DSD before the initiation of estrogen treatment.