Background: Among several candidate genes that promote peritoneal dissemination extracted by comprehensive expression analysis of both in vivo selected metastatic cell lines and patients with gastric cancer, we focused on the chemokine (C-X-C motif) receptor (CXCR7) and explored its clinicopathological significance in gastric cancer. Methods:CXCR7 expression was evaluated by microarray data in the Singapore cohort (n = 196) and by immunohistochemistry and reverse transcription quantitative real-time polymerase chain reaction in the Japanese cohort (n = 195). The biological function of CXCR7 in gastric cancer was explored using gene set enrichment analysis (GSEA). Results: CXCR7 expression was upregulated in tumor tissues compared to normal tissues. High CXCR7 mRNA expression was associated with peritoneal dissemination and poor prognosis in the Singapore cohort. Consistent with this, the high CXCR7 mRNA expression group showed significantly poorer prognosis and a more aggressive disease course than the low expression group in the Japanese cohort. High CXCR7 mRNA expression and peritoneal dissemination were clinically relevant. GSEA revealed that CXCR7 was significantly enriched in gene expression signatures associated with tumor progression. Conclusions:CXCR7 may be a prognostic indicator and therapeutic target for gastric cancer with peritoneal dissemination.