Walk-in open access in general practice may influence the general practitioner's (GP's) work, but very little research has been done on the consequences. In this study from Danish general practice, we compare the prevalence of burnout between GPs with a walk-in open access and those without. In a questionnaire study (2004), we approached all 458 active GPs in the county of Aarhus, Denmark, and 376 (82.8%) GPs returned the questionnaire. Walk-in open access was defined as at least 30 minutes every weekday where patients could attend practice without an appointment. Burnout was measured by the Maslach Burnout Inventory. Analyses using logistic regression were adjusted for gender, age, marital status, job satisfaction, minutes per consultation, practice organisation, working hours, number of listed patients per GP, number of contacts per GP, continuing medical education- (CME-) activities, and clusters of GPs. In all, 8% of GPs had open access and the prevalence of burnout was 24%. GPs with walk-in open access were more likely to suffer from burnout. Having open access was associated with a 3-fold increased likelihood of burnout (OR = 3.1 (95% CI: 1.1-8.8, P = 0.035)). Although the design cannot establish causality, it is recommended to closely monitor possible negative consequences of open access in general practice.