CONTEXT: Pheochromocytoma and sympathetic paraganglioma (PPGL) are rare catecholamine-secreting tumors but recent studies suggest increasing incidence. Traditionally, PPGL are described to present with paroxysmal symptoms and hypertension, but existing data on clinical presentation of PPGL come from referral centers. OBJECTIVE: We aimed to describe time trends in clinical presentation and incidence of PPGL in a population-based study. METHODS: We conducted a nationwide retrospective cohort study of a previously validated cohort of 567 patients diagnosed with PPGL in Denmark 1977-2015. We collected clinical data from medical records of a geographic subcohort of 192 patients. We calculated age-standardized incidence rates (SIRs) and prevalence for the nationwide cohort and descriptive statistics on presentation for the subset with clinical data. RESULTS: SIRs increased from 1.4 (95% CI 0.2-2.5) per million person-years in 1977 to 6.6 (95% CI 4.4-8.7) per million person-years in 2015, corresponding to a 4.8-fold increase. The increase was mainly due to incidentally found tumors that were less than 4 cm and diagnosed in patients older than 50 years with no or limited paroxysmal symptoms of catecholamine excess. On December 31, 2015, prevalence of PPGL was 64.4 (CI 95% 57.7-71.2) per million inhabitants. Of 192 patients with clinical data, 171 (89.1%) had unilateral pheochromocytoma, while unilateral paraganglioma (n = 13, 6.8%) and multifocal PPGL (n = 8, 4.2%) were rare. CONCLUSION: Incidence of PPGL has increased 4.8-fold from 1977 to 2015 due to a "new" group of older patients presenting with smaller incidentally found PPGL tumors and few or no paroxysmal symptoms.