The carbohydrated antigen Ca-125 is identified by Bast et al. in 1981. The cut off value of 35 KU/l for serum levels of the marker covers in fact 98-99% of the healthy women. There are some variations in the levels of pre- and post menopausal women, and also some race- dependent and cycle-dependent differences. Although Ca-125 is the only one accepted tumor marker for ovarian cancer, its screening usage is controversial, because of the high percentage of false positive results. Ca-125 and HE4 are both validated serum markers for differential diagnose of pelvic masses. The Ca-125 main role is monitoring patients, having ovarian cancer in their chemotherapy, early recurrence finding and progression. Ca-125 rising values in monitoring patients are predictor of image or clinical recurrence in 59-96% of the cases. FDG PET/CT gave a new standard in ovarian cancer staging, especially in patients, having high levels of Ca-125, but negative conventional imaging examinations.