Background: We recently showed that cancer cells, with proliferative and tumorigenic potential, can spill into the peritoneal cavity during curative (R0) gastric cancer (GC) surgery, which is associated with peritoneal recurrence (PM). To elucidate the pathophysiology of PM, the relationship between spilled cancer cells and cancer stem cells was evaluated. Furthermore, to identify a therapeutic strategy for PM, the prognostic impact of hyperthermic intraperitoneal chemotherapy (HIPEC) following GC surgery with spillage of cancer cells was evaluated. Methods: Patients with advanced GC (≥pT2 [MP]) who underwent R0 gastrectomy between 2010 and 2015 were enrolled. Ninety-four consecutive patients with negative results in peritoneal cytology and cancer cell culture (CCC [-]) following peritoneal washing (PW) before GC surgery were included. Spilled cancer cells in PW after GC surgery (PW-Post) were examined to identify any CD44-positive cancer stem-like cells associated with cancer metastasis. Based on the PW-Post CCC results, associations between HIPEC and recurrence-free survival (RFS), or overall survival (OS) were evaluated. HIPEC was performed following GC surgery using CDDP, MMC, and 5-FU in 5 L saline maintained at 42^˚C for 30 min. Results: Spilled cancer cells included CD44⁺ cancer stem-like cells. In 48 patients with PW-Post positive CCC (CCC [+]), the number of patients with pStage I, II, and III were 4, 7, and 15, respectively, in those who received HIPEC (n = 26), and 3, 9, and 10, respectively, in those who did not (n = 22). Among patients with CCC (+), the 5-year peritoneal RFS, hepatic RFS, and lymph node RFS rates were 93.3%, 100%, and 68.5%, respectively, in patients who received HIPEC, and 56.7%, 35.6%, and 66.7%, respectively, in those who did not (P = 0.008, P = 0.008, and P= 0.24, respectively). Among patients with PW-Post CCC (-), none developed recurrence, regardless of whether they received HIPEC (n = 28) or not (n = 18). Conclusions: The results show that PW-Post CCC is a promising predictive biomarker for recurrence after R0 GC surgery. Adjuvant HIPEC performed with R0 GC surgery showed preventive effects on peritoneal and hepatic recurrence and survival benefits for patients with PW-Post CCC (+).