Background: The aim of this study was to describe healthcare utilization of patients admitted to ICU before and after ICU admission. Methods: Register-based study including adult patients discharged from ICU between January 1st, 2011 and December 31st, 2014. Reference group was a sex- and age-matched population not admitted to an ICU in the study period. Outcomes were hospital admissions, contacts to general practitioner or emergency services and municipality services from 1 year before ICU admission and up to 3 years after. Results: The study included 82 384 patients and an equal number of reference persons. Of patients with ICU admission, 48% were married (reference group 57%), 48% had elementary school education (reference group 38%) and 18% had a Charlson co-morbidity score of 5+ (4% in reference group). We found that 51% of patients with an ICU admission had been admitted to hospital in the year before ICU admission (reference group 15%) and 97% had a contact to a general practitioner (reference group 89%) in the same period. Conclusions: Patients admitted to an ICU had increased use of both primary and secondary health care both before and for years after ICU treatment, even after adjustment for comorbidities and socio-economic factors.