Approximately 85% of patients with advanced ovarian cancer will experience recurrence of the disease. In 311 patients CA125 serum levels were determined at follow up investigation in our department. A sensitivity of 92% and specificity of 89% were calculated. Reflecting the further course of disease, specificity could be increased up to 97%. Using 25 U/ml/month as the upper limit of grade of CA125 increase, a 100% specificity for detecting recurrence could be achieved. In conclusion, recurrence diagnosis and even therapy should be started in cases of either significantly raised CA125 levels or elevated grade of CA125 increase.