Endometriosis has been defined as the presence of endometrial tissue (gland and stroma) outside the inner lining of the endometrium. The lesion has been associated with debilitating and bizarre clinical features and in the absence of histopathologic assessment may result in severe consequences to the patient. Specifically, albeit rare, there is the possibility of malignant transformation. Therefore, this presentation on endometriosis as an unusual occurrence is of ardent import to health personnel, especially as regard to the requirements for in-depth intra/interdisciplinary consultation in general and the role of the pathologist, specifically in management of cases. Materials and methods. This was the case of a 30-year-old self-employed nulliparous female who was referred from a secondary health facility due to abdominal swelling of eight-month duration. The swelling was progressive and associated with an unproductive cough, chest pain, weight loss and dysmenorrhoea. The patient was subjected to clinical examination, haematologic review, radiologic assessment and histopathologic investigations. Results. The examination revealed dull percussion notes, reduced air entry into both right and left thoracic lung fields with bilateral crepitations in both lung fields. The abdomen was distended with massive ascitic fluid. The patient was stabilized and, consequently, an exploratory laparotomy demonstrated endometrial glands in the follicular phase with the associated stroma in the right ovaries. In sections of the omentum, there were endometrial glands and stroma, some of them were cystically dilated, filled with fluid and cellular debris in their lumen. Contribution to knowledge. This study has established the existence of endometriosis in a woman in her reproductive years further substantiating the multiple distribution presentation, debilitating nature and the role of histopathologic input in management of this lesion.