Background: Struma ovarii is a rare ovarian neoplasm, which contains thyroid tissue. It accounts for less than 5% of ovarian teratomas. These are mostly benign, occurring between 40 years and 60 years of age. Clinical and radiological features are inconclusive and mostly it is diagnosed by histopathology. About 5–8% cases have hyperthyroidism. Cystic struma ovarii is very rare with only 25 cases reported till now. It creates confusion in diagnosis, as even in histopathology, the cells are mostly like those resembling other cystic ovarian tumors with minimal thyroid follicles. Case description: A 20-year-old girl came with complaints of abdominal discomfort and difficulty in squatting and lying supine. Clinically, a 28-week-size cystic tumor was palpated. Ultrasound showed features of a cystic benign tumor. Tumor markers were normal. Laparoscopic cystectomy was done. Histopathology showed cystic struma ovarii. At 6-month follow-up, the patient has been doing well. Conclusion: Cystic struma ovarii is a rare diagnosis. Clinical, biochemical, and radiological features do not help. A careful and keen pathological examination is necessary so that thyroid follicles are not left while viewing. There is no clear consensus on follow-up of these patients, but benign tumors usually do not need extensive follow-up. Clinical significance: It is a rare tumor and a good histopathological diagnosis is needed. Cystic tumors should be carefully examined. A proper correlation between clinical, biochemical, radiological, intraoperative, and histopathological findings may help us to consider this diagnosis when we get similar cases.