Objective: To determine whether there were differences in presentation, imaging, and tumour markers between pediatric and adolescent gynaecology patients with adnexal masses managed expectantly and those managed surgically. Methods: We conducted a retrospective review of patients who presented to the pediatric and adolescent gynaecology service with adnexal masses between January 2003 and January 2006 at Toronto's Hospital for Sick Children. We used t tests, chi-square, and Pearson correlation tests for analysis. Results: We identified 114 patients with an adnexal mass. Fifty-nine percent had surgery (laparotomy 41.8%, laparoscopy 58.2%) and 41% were managed conservatively. The mean age of patients was 12.7 years (range 7 days to 18 years) and there was no difference in age between management groups (P = 0.59). The most common presenting symptom was abdominal pain (72.8%). Increased abdominal girth was found only in the surgical group (P < 0.01). Size of the mass was the only feature on imaging that differed between groups (11.1 cm surgical vs. 5.3 cm observed, P < 0.001). CT scans were performed in 35 patients, 94.3% of whom had surgery (P < 0.001). Tumour markers were drawn in 41.2% of patients, more often in surgical patients (P < 0.001), and 27% were abnormal, all in the surgical group. Surgical approaches included cystectomy, oophorectomy, or detorsion. Twelve percent of surgeries were for malignancies, representing 7.0% of all adnexal masses, and malignant masses were larger than benign masses (16.1 cm vs. 10.5 cm, P < 0.05). In cases that required only expectant management with serial ultrasound, both simple and complex masses resolved, with or without hormonal suppression. Conclusion: Larger masses and masses associated with increased abdominal girth or abnormal tumour markers were more likely to be managed by surgical intervention. Surgically managed patients had more investigations. Forty-one percent of masses in patients referred to pediatric and adolescent gynaecology specialists resolved with expectant management.