Background: Primary umbilical endometriosis is a rare form of cutaneous endometriosis occurring without prior surgical intervention and often mimics other benign or malignant umbilical lesions.

Case Presentation: A 34-year-old nulliparous woman presented with a solitary umbilical nodule of six months’ duration associated with mild pain and occasional spontaneous bleeding. There was no history of prior abdominal surgery. Examination revealed a 2 cm firm, well-defined, dark-brown nodule within the umbilicus. Differential diagnoses included keloid, pyogenic granuloma, metastatic deposit, and cutaneous endometriosis. Routine investigations and pelvic ultrasonography were normal. Histopathology demonstrated endometrial glands lined by simple columnar epithelium surrounded by endometrial-type stroma, confirming the diagnosis.

Conclusion: Primary umbilical endometriosis should be considered in the differential diagnosis of umbilical nodules in women of reproductive age. Histopathological confirmation is essential, and complete surgical excision is curative.