The prognostic significance of the number of lymph nodes examined in surgical specimen of colorectal cancer was determined. One thousand and twenty five patients with colorectal cancer stage II and III were included in the study. These patients underwent surgery from 1991 to 1997 and were enrolled in clinical trials to evaluate the efficacy of adjuvant 5-fluorouracil (5FU) based chemotherapy. The median number of examined lymph nodes was five. Only 13% of the patients had > or = 12 lymph nodes analyzed. The number of examined lymph nodes was an independent prognostic factor for overall survival in the entire group of patients with stage II and III colorectal cancer (p=0.009). Patients with a higher number of lymph nodes examined had a longer overall survival. In stage III colorectal cancer the ratio of the number of metastatic lymph nodes to the number of examined lymph nodes (lymph node ratio, LNR) was an independent prognostic factor for overall survival. A decreasing LNR was correlated with a longer overall survival (p<0.0001). Increasing age was associated with a reduction of lymph node harvest (p=0.04). Patients with rectal cancer treated with preoperative radiotherapy had a lower number of lymph nodes analyzed compared with non-radiated (p<0.001). The number of examined lymph nodes in the surgical specimen is an independent prognostic factor for overall survival in colorectal cancer. The LNR is an independent prognostic factor in stage III colorectal cancer.