Background: Gonadal dysgenesis encompasses a variety of sexual differentiation disorders. Within this population of patients, there is an increased risk of gonadal tumor formation. Cases: In this case series of three patients, two with Swyer's syndrome (complete gonadal dysgenesis) and one with mosaic Turner's syndrome, three separate histologic subtypes of tumors were identified: dysgerminoma, seminoma, and gonadoblastoma. The patients with dysgerminoma and seminoma had regular menses and were without recurrent disease. We recommend that the patient with gonadoblastoma start on hormone therapy. Conclusion: Once the diagnosis of gonadal dysgenesis is made, prophylactic gonadectomy should be performed owing to the probability of malignant transformation. These patients illustrate the potential different presentations with gonadal dysgenesis and the importance of complete evaluation of patients with primary amenorrhea.