A 22-year-old known case of 45XO/46XY mixed gonadal dysgenesis, reared as a male, presented with complaints of suprapubic and left iliac fossa pain for the past 1 month. The patient underwent laparoscopic right orchidectomy (streak) + Mullerian remnant excision + left orchidopexy + first-stage hypospadias repair 10 years back. Contrast-enhanced computed tomography showed a large complex cyst in the left side of the pelvis and rectovesical space. Excision of the cystic structure was done along with left orchidectomy. Histopathological examination revealed features of Mullerian remnants (endometrial glands and cervix) in the cystic structure. The importance of this case report is to emphasize the fact that the Mullerian remnants tend to enlarge in size over time and become symptomatic and may require a surgical removal at a later date as in our case.