Background and Objectives: The diagnosis of pregnancy associated adnexal masses is rising due to routine utilization of sonography in prenatal care. The purpose of this study was to describe pregnancy associated adnexal masses over a period of 10 years. Patients and Methods: A retrospective study was reviewed hospital records of all pregnant women with adnexal mass that underwent surgical resection in Mirza Kuchak Khan Hospital in Tehran from January 1996 to March 2006. The collected data included maternal age, parity, gestational age at diagnosis, surgery and delivery, presenting symptoms and treatment. The pregnancy outcome complications and histological findings were reviewed. Results: Totally 29220 deliveries were performed in our institution; adnexal masses were detected in 0.01% of pregnancies. Antepartum surgery was performed in 4 (10.3%) patients. The mean gestational age at delivery in patients undergoing surgery during pregnancy was 36 weeks (ranged 36-37 weeks) while in patients with cystectomy during cesarean delivery was 38 weeks (range: 33-40) (P=0.04). There were no statistically significant differences in birth weight between the patients undergoing surgery during pregnancy and those with surgery at cesarean delivery (P=0.176). The mean cyst diameter was 11 cm (range 4-16 cm) for patients operated during pregnancy while it was 4 cm (2.5-12 cm) for those undergoing surgery during cesarean delivery (P=0.006). The most common diagnosis was benign serous cyst (23.1%) followed by benign Dermoid cyst (20.5%). Conclusion: Patients undergoing laparotomy for adnexal mass during pregnancy had higher risk of preterm labor but there were no difference in birth weight.