This study was designed to prospectively examine whether the presence of occult neoplastic cells (ONCs) in lymph nodes or positive high-risk (HR) criteria were related to the survival of patients with stage II/III colorectal cancer or gastric cancer. The 3-year relapse-free survival (3Y-RFS) rate was calculated for 79 patients who were registered during a 2-year period. The 3Y-RFS rate was 80.5% in patients without ONCs (n=54) and 84.3% in patients with ONCs (n=25; p=0.9089). Among patients who had stage II/III colorectal cancer, it was 89.0% (n=47) and 76.2% (n=15), respectively (p=0.4131). For patients with stage III colorectal cancer alone, it was 80.8% (n=24) and 62.5% (n=9), respectively (p=0.4006). The 3Y-RFS rate was respectively 88.1% and 77.6% for the HR patients (n=31) and low-risk (LR) patients (n=48) with stage II/III colorectal cancer or gastric cancer (p=0.5545). It was respectively 92.3% and 84.3% for the HR patients (n=20) and LR patients (n=42) with stage II/III colorectal cancer (p=0.5073). Also, the rate was respectively 80% and 76.2% for the HR patients (n=7) and LR patients (n=26) with stage III colorectal cancer alone (p=0.9506). These results indicate that the 3Y-RFS rate is lower in ONC-positive patients with stage II/III colorectal cancer, suggesting that ONCs may have an influence on survival.