OBJECTIVE. This study examined whether age, gender, and comorbidity were of importance for an individual's choice of listing with either a public or a private primary health care (PHC) practice. DESIGN AND SETTING. The study was a register-based closed cohort study in one private and one public PHC practice in Blekinge County in southern Sweden. Subjects. A cohort (12 696 individuals) was studied comprising all those listed with the public or private PHC practice on 1 October 2005 who were also listed with the public PHC practice on 1 October 2004. MAIN OUTCOME MEASURES. The listing/re-listing behaviour of the population in this cohort was studied at two points in time, 1 October 2005 and 1 October 2006, with respect to age, gender, and comorbidity level as measured by the ACG Case-Mix system. RESULTS. Individuals listed with the public practice both on 1 October 2005 and one year later were significantly older, were more often females, and had a higher comorbidity level than individuals listed with the private practice. Individuals with a higher comorbidity level were more likely to re-list or to stay listed with the public practice. CONCLUSIONS. This study shows that the probability of choosing a public instead of private PHC provider increased with higher age and comorbidity level of the individuals. It is suggested that using a measure of comorbidity can help us understand more about the chronically ill individual's choice of health care provider. This would be of importance when health care policy-makers decide on reimbursement system or organization of PHC.