Background: Treating patients with anorexia nervosa (AN) remains a major challenge. The choice between an inpatient or an outpatient care setting is an essential issue for the patients and for their relatives with major health economic implications. However, health services-related studies are lacking. The present study was a descriptive exploration of time-trends in treatment modes of patients with free and equal access to health services. Methods: The study was based on a nationwide cohort of patients diagnosed for the first time with AN, each followed for 5 years in the registers covering the years 1994–2018. The per patient number of hospital admissions, cumulated number of days of hospitalization and number of outpatient visits during the first 5 years after initial diagnosis were considered. Results: The cohort of patients with AN with at least 5 years of follow-up amounted to N = 7,505. A clear trend was observed in the per patient five-year cumulated number of inpatient days, decreasing by 6% per year after adjustment for age at diagnosis, parental mental diagnosis, and family income. The five-year number of hospital admissions after initial diagnosis decreased by 2% per year, while no trend was observed for outpatient visits. Conclusions: The per patient number of hospitalizations and cumulated days of hospitalization during 5 years after diagnosis were reduced for patients initially diagnosed with AN while there was no change in the number of outpatient visits. The factors contributing to these changes of treatment modes over time are in need of further study.