Background: Viral or idiopathic pericarditis is a frequent condition, often considered benign, although prior studies have suggested that pericarditis is associated with both cardiovascular and noncardiovascular disease, for example, malignancy. Objectives: This study sought to assess mortality risk and morbidity patterns in patients with incident viral or idiopathic pericarditis. Methods: In nationwide Danish registries, we identified patients discharged with a first-time diagnosis of pericarditis from 1996 to 2016. Patients with a severe underlying heart condition were excluded. The patients were matched 1:10 with individuals from the general population by sex and year of birth. We assessed 5-year mortality using Kaplan-Meier and Cox proportional hazards models adjusted for baseline comorbidities and identified subsequent hospital admissions. Results: We identified 7,988 patients with pericarditis and 79,880 matched control individuals. The absolute 5-year survival probability was 92.9% and 95.8% in the pericarditis and control groups, respectively (adjusted hazard ratio: 1.31; 95% confidence interval: 1.13 to 1.52). The greatest difference in mortality was seen the first year, and it was primarily driven by the female part of the population. The incidence rate per 1,000 person-years of new-onset, admission-required diagnosis was higher in the pericarditis group both for cardiovascular and noncardiovascular diseases. Conclusions: We observed a higher mortality risk over 5 years in the pericarditis group, especially among the female patients, compared to matched control individuals. Furthermore, we observed a higher frequency of both cardiovascular and noncardiovascular hospital admissions, highlighting the need for focus on underlying morbidity in patients presenting with apparent viral or idiopathic pericarditis.