Objectives To keep healthcare systems sustainable for future demands, many countries are developing a centralised telephone line for out-of-hours primary care services. To increase the quality of such services, more information is needed on factors that influence caller satisfaction. The aim of this study was to identify demographic and call-related characteristics that are associated with the patient satisfaction of callers to a medical helpline in Denmark. Design Retrospective cohort study on patient registry data and questionnaire results. Setting Non-emergency medical helpline in the Capital Region of Denmark. Participants A random sample of 30 402 callers to the medical helpline between May 2016 and May 2018. Primary and secondary outcome measures Responses of a satisfaction questionnaire were linked to demographic and call-related dispatch data. Associations between the characteristics were analysed with multivariable logistic regression analysis with satisfaction as the dependent variable. A subgroup analysis was performed on callers for children aged between 0 and 4 years. Results Of the 30 402 analysed callers, 73.0% were satisfied with the medical helpline. Satisfaction was associated with calling for a somatic injury (OR: 1.96, 95% CI: 1.72 to 2.23), receiving a face-to-face consultation (OR: 2.27, 95% CI: 2.04 to 2.50) and a waiting time less than 10 min (OR: 1.82, 95% CI: 1.56 to 2.08). Callers for a 0-year to 4-year-old patient were more likely to be satisfied when they called for a somatic illness or received a telephone consultation, compared with the rest of the population (p<0.0001). Conclusion Callers were in general satisfied with the medical helpline. Satisfaction was associated with reason for encounter, triage response and waiting time. People calling for 0-year to 4-year-old patients were, compared with the rest of the population, more frequently satisfied when they called for a somatic illness or received a telephone consultation.