Despite chemotherapy and intended curative surgery, approximately 50% of patients with gastric cancer develop recurrence and eventually die of metastatic disease. The detection of circulating tumour cells (CTC) in peripheral blood is a promising prognostic and predictive marker. The most typically applied approaches to the detection of CTC are RT-PCR and immunological assays. Measurement of CTC in gastric cancer seems useful for predicting prognosis and monitoring response of chemotherapy. There is still no gold standard for CTC-detection in gastric cancer patients and larger studies are needed.