Background: Long-term follow-up studies of adults with well-characterized asthma are sparse. Objective: We aimed to examine long-term remission and change in disease severity over 30 years in adults with asthma. Methods: A total of 125 individuals diagnosed with asthma between 1974 and 1990 at a Danish respiratory and allergy clinic, based on history and objective assessments, were included. At follow-up (2017-2019), participants completed questionnaires and had spirometry, bronchodilator reversibility, airway responsiveness, and blood biomarkers measured. Based on these assessments, participants were classified as having either active asthma, clinical remission (no symptoms or prescribed asthma medication within the last year), or complete remission (fractional exhaled nitric oxide <50 parts per billion, no bronchodilator reversibility, no airway hyperresponsiveness, and no airflow limitation). Changes in severity were determined according to Global Initiative for Asthma guidelines based on symptom control and currently prescribed medication. Results: At follow-up, 25% (n = 31) and 15% (n = 19), respectively, had clinical and complete remission. Our analyses showed that a longer duration of symptoms before the initial assessment (odds ratio, 0.86; 95% confidence interval, 0.75-0.98) was associated with a lower chance of asthma remission. At follow-up, 30% had well-controlled asthma compared with none at baseline. Female sex, previous severe exacerbation(s), and older age at baseline were associated with uncontrolled asthma at follow-up. Blood-eosinophil count (≥0.3 × 10⁹/L) and prescribed inhaled corticosteroid (ICS) at baseline were associated with being prescribed medium/high-dose ICS at follow-up. Conclusion: Despite 30 years of follow-up, asthma rarely remits in adults, especially in individuals with longer duration and presumably more severe disease. Initial signs of pronounced disease activity were associated with uncontrolled asthma at follow-up.