Purpose Controversy exists regarding the extent to which lymph node dissection (LND) should be performed for operable colorectal cancers (CRCs) during primary surgical resection. We reappraised the role of LND in CRCs. Methods Seventy-three CRC patients (mean age, 65.3 years; 43 males) undergoing primary surgical resection at Taipei Hospital, Ministry of Health and Welfare, Taiwan, within a 3-year period were retrospectively analyzed. Their pathological T/N/M statuses and cancer stages were defined according to the American Joint Committee on Cancer (AJCC) 8th edition staging system. The numbers of total dissected lymph nodes (TDLNs), positive dissected lymph nodes (PDLNs), and negative dissected lymph nodes (NDLNs) for each CRC patient were recorded in detail (TDLNs = PDLNs + NDLNs). Possible prognostic variables were evaluated. Results An advanced N status (N1/N2 vs. N0; HR, 5.749/17.677 vs. 1.000; p = 0.056/0.009) and M1 status (M1 vs. M0; HR, 7.517 vs. 1.000; p = 0.010) were independent variables for a poor prognosis. For all 73 CRC patients (p = 0.030), as well as T2 CRC patients (p = 0.061), those with > 15 TDLNs tended to have more PDLNs than those with ≤ 15 TDLNs. For 42 N(+) CRC patients (p = 0.007), as well as N2 CRC patients (p = 0.011), those with > 21 TDLNs tended to have more PDLNs than those with ≤ 21 TDLNs. Conclusion For CRC patients undergoing primary surgical resection, the number of TDLNs influences the accuracy of nodal staging. A minimum of 15 TDLNs is necessary for positive lymph nodes to be identified in CRC patients, and 21 TDLNs is sufficient for the severity of the N(+) status to be distinguished in N(+) CRC patients.