We describe two cases of large solitary luteinized follicle cyst of pregnancy and puerperium (LSLFCPP) with new clinicopathologic findings. The first case occurred in a 40-year old woman who was found to have a left ovarian mass during the third trimester of pregnancy. The patient delivered a full term healthy female infant via caesarean section. The ovarian mass was removed by oophorectomy. The specimen showed a unilocular, thin-walled, clear fluid filled cyst measuring 15 × 12 × 5 cm. Microscopically, the cyst was lined by single to multiple layers of luteinized cells with mainly small, round and regular nuclei and focally enlarged, bizarre, and hyperchromatic nuclei. Occasional mitotic figures were seen. The cyst wall showed marked edema and nests of luteinized cells that were morphologically similar to the cyst lining cells. Groups of lesional cells were surrounded by reticulin fibers. The patient has been healthy without disease after 7 years. The second patient was a 29-year old pregnant woman who was found to have a right ovarian cyst by ultrasound at 14-week gestation. She then presented with preterm labor at 33-week gestation and delivered a healthy female infant via caesarean section. A right salpingo-oophorectomy was performed. Gross inspection of the specimen revealed a unilocular, brown mucoid fluid filled cyst measuring 14 × 11 × 9 cm. The cyst surfaces were smooth, and the cyst wall exhibited marked edema. Microscopic examination showed features similar to the first case: cyst lined by luteinized cells with focal large nuclei, scattered nests of luteinized cells in the edematous fibrous wall, and reticulin fibers surrounding large nests of lesional cells. No mitoses, however, were identified in the second case. The patient has been well without disease 1 year after surgery. These two cases contribute to a better understanding of LSLFCPP. Our case in the 40-year old patient is the first to show mitotic figures in LSLFCPP and suggests that the presence of occasional mitoses should not exclude a diagnosis of LSLFCPP. The lesion in the second patient caused preterm labor. Nevertheless, absence of disease recurrence in our patients demonstrates a benign nature of LSLFCPP.