BACKGROUND & AIMS: Perianal Crohn's disease (CD) is characterized by fistulae and/or abscesses in the anal region and leads to significant morbidity. We aimed to estimate the incidence and describe the disease course of perianal disease in pediatric-onset CD. METHODS: In a nationwide registry-based study, we included patients diagnosed with pediatric-onset CD (<18 years) between 1980 and 2018. Cumulative incidence of perianal disease was calculated. Cox regression was used to assess the risks of major abdominal surgeries, colorectal cancer, and mortality. Hazard ratios were adjusted (aHR) for sex, family income, and year of CD diagnosis. RESULTS: We identified 2356 patients with pediatric-onset CD, of whom 769 (32.6%) developed perianal CD. The cumulative incidence of perianal CD was 14.0%, 21.1%, and 28.1% after 1, 5, and 10 years. The incidence rate was 28.8 per 1000 person-years (95% confidence interval [CI], 26.8-30.9), corresponding to 45.2% after 30 years. Perianal abscesses developed in 460 patients (59.8%) and fistulas in 399 (51.9%). When comparing patients with/without perianal disease, the aHR for major abdominal surgery, cancer, and mortality were 1.5 (95% CI, 1.3-1.8), 0.8 (95% CI, 0.2-2.7), and 1.5 (95% CI, 0.9-2.7). A stoma was required in 308 (40.1%) and 147 (9.3%) patients with and without perianal disease, respectively (aHR, 2.8; 95% CI, 2.3‒3.4). Of mortalities, 35 had perianal disease (4.6%; mortality rate, 2.2/1000 person-years) and 33 did not (2.1%; mortality rate, 1.4/1000 person-years). CONCLUSION: We report a high incidence of perianal disease in pediatric-onset CD. Patients with perianal disease had higher risks of major abdominal surgery and requiring stomas than patients without perianal CD.