The most frequent cause of treatment failure following surgery for gastric cancer is peritoneal metastasis. The ability to predict the likelihood of peritoneal recurrence should improve the therapeutic approach to gastric cancer. Cytological analysis of peritoneal washings is thought to be useful for direct detection of free cancer cells in the peritoneal cavity. Intraperitoneal free cancer cells (IFCC) isolated during peritoneal washing in patients with gastric cancer, have been demonstrated to be significantly and independently related to the prognosis, influencing both early recurrence and poor survival, so that since 1998 the Japanese Classification of Gastric Carcinoma (JCGC) recommend peritoneal wash cytology (PWC) for the local staging. In Western countries PWC is not uniform practice, because of several controversies regarding the low sensitivity rate of conventional cytology, the correct application of molecular diagnosis (immunostaining and RT_PCR) and the exact role of PWC in the clinical practice. The authors examine the current apply of peritoneal washing in gastric cancer, emphasizing the clinical implication of peritoneal cytology by analyzing the different modality and techniques to perform it (conventional cytology, immunocytochemistry, RT-PCR), when to achieve it during the diagnostic or clinical work-up (at the staging or during the surgical treatment), and who will get a benefit (all patients or selected patients).