Purpose: To determine whether the presence of normal ovarian tissue could assist in the diagnosis of large benign ovarian neoplasms in young females and in choosing the laparoscopic treatment. Materials and Methods: A prospective study of 25 patients treated surgically for a cystic ovarian neoplasm measuring diameter more than ten cm or volume more than 500 ml and having normal ovarian tissue or ovarian crescent sign (OCS). Ultrasonography was performed at six weeks, then at three, six, nine, and 12 months postoperatively. Results: The mean age of patients was 15.3 ± 3.6 years, ranging between 6.5 and 19 years. The mean preoperative volume of the ovarian neoplasm was 1,686 ± 1,380 cm3, ranging between 550 and 6,000 cm3. The presence of OCS was visualized by ultrasonography in all 25 patients and serum tumor markers were negative in 22. No borderline tumors or malignancies were identified. There was a statistically significant difference between the volume of the affected ovary and the contralateral ovary during the first six weeks follow-up, but without significant difference after three months. Conclusions: Postoperative ultrasound revealed that the affected ovary resumed its normal volume within three months after surgery, despite the thinned appearance of the ovarian cortex present on ultrasound as the OCS. Laparoscopic ovarian preservation should be the preferred surgical approach for adolescents to ensure the conservation of the entire ovarian tissue.