The invention relates to a method and means for diagnosing tumors, in particular for an early diagnosis (prevention) and for differentiating between benign and malignant tumors using a PCR, in particular in bodily fluids. The method according to the invention is characterized by a combination of a pre-amplification process using a PCR, wherein methylated DNA sequences are amplified more strongly than non-methylated DNA sequences, and a subsequent quantification process using a special digital PCR, in which significantly more DNA is used than normally in the prior art. As comparison data indicates, the invention advantageously allows a clear reliable conclusion as to whether a malignant tumor disease is present or not. The invention is suitable for screening (prevention), monitoring the progress of a tumor disease, in particular to order to exclude a minimal residual disease (MRD), and for a differential diagnosis between malignant carcinoma and benign tumors.