Background: Most cancer diagnostic pathways initiate from primary care and several factors affect the diagnostic processes. Aim: To analyse the associations between patient characteristics, symptom presentation and cancer type and the general practitioner’s (GP’s) assessment of the diagnostic processes. Design and setting: General practices in the North, Central, and Southern regions of Denmark were invited to participate in a questionnaire survey. Methods: Participating GPs received a list of incident cancer patients within a two-year period based on regional hospital data. A questionnaire was completed for each patient, addressing symptom presentation and the GP’s assessment of the diagnostic process both overall and in four subcategories (the patient’s, and the GP’s role, the transition between primary and secondary care, and the secondary sector’s role). Results: A total of 187 general practices informed on 8,240 patients. For 5,868 patients, diagnostic pathways started in general practice. Almost half (48%) presented with specific cancer symptoms. GPs assessed 56% and 32% of the diagnostic processes as “very good” and “predominantly good”, respectively; 12% were “predominantly poor” or “very poor”. Long symptom duration of 2+ months before GP contact and presenting with non-specific or a combination of non-specific and specific symptoms were associated with a poor overall assessment of the diagnostic process. Assessment in the four subcategories showed that the patient’s role was assessed less positively than the other three categories. Conclusion: A longer symptom duration and presenting without cancer-specific symptoms were associated with GPs assessing the diagnostic process as poor.