OBJECTIVE: The view that the general practitioner (GP) should be more involved during the curative treatment of cancer is gaining support. This study aimed to assess the current role of the GP during treatment of patients with colorectal cancer (CRC). DESIGN: Historical prospective study, using primary care data from two cohorts. SETTING: Registration Network Groningen (RNG) consisting of 18 GPs in three group practices with a dynamic population of about 30,000 patients. SUBJECTS: Patients who underwent curative treatment for CRC (n = 124) and matched primary care patients without CRC (reference population; n = 358). MAIN OUTCOME MEASURES: Primary healthcare use in the period 1998-2009. FINDINGS: Patients with CRC had higher primary healthcare use in the year after diagnosis compared with the reference population. After correction for age, gender, and consultation behaviour, CRC patients had 54% (range 23-92%) more face-to-face contacts, 68% (range 36-108%) more drug prescriptions, and 35% (range -4-90%) more referrals compared with reference patients. Patients consulted their GP more often for reasons related to anaemia, abdominal pain, constipation, skin problems, and urinary infections. GPs also prescribed more acid reflux drugs, laxatives, anti-anaemic preparations, analgesics, and psycholeptics for CRC patients. CONCLUSIONS: The GP plays a significant role in the year after CRC diagnosis. This role may be associated with treatment-related side effects and psychological problems. Formal guidelines on the involvement of the GP during CRC treatment might ensure more effective allocation and communication of care between primary and secondary healthcare services.