BACKGROUND Lymphangioma is an atypical non-malignant, lymphatic lesion that is congenital in origin. Lymphangioma is most frequently observed in the head and neck, but can occur at any location in the body. About 65% of lymphangiomas are apparent at birth, while 80-90% are diagnosed by two years of age. Occurrence in adults is rare, as evidenced by less than 100 cases of adult lymphangiomas reported in the literature. CASE REPORT A 36-year-old Indian woman with a medical history of recurrent pleural effusions presented with chief complaints of dyspnea on exertion for one year and a low-grade fever for one month. A thorax CT revealed left-sided pleural effusion with thin internal septations. Thoracoscopy revealed a large cystic lesion arising from the mediastinum from the hilum surrounding the mediastinal great vessels. The diagnosis of lymphangioma was confirmed via histopathologic examination of the cyst. It was managed with partial cystectomy along with the use of a sclerosing agent (talc). CONCLUSIONS The size and location of lymphangiomas can vary, with some patients presenting with serious problems like respiratory distress, while others may be asymptomatic. Complete cyst resection is the gold standard treatment for mediastinal cystic lymphangioma. Partial cyst resection along with the use of sclerosing agents can be an effective option when complete cystectomy is not possible. Although lymphangioma is a rare patient condition, it should be included in the differentials for patients presenting with pleural effusions. Also, a biopsy should be done at the earliest opportunity to differentiate lymphangioma from other mediastinal malignant tumors.