Acute herpetic gingivostomatitis is an acute viral infection of the gingiva caused by herpes simplex virus-1. It typically affects children ages 6 months to 6 years, initially forming numerous vesicles that rupture into painful shallow ulcers covered by yellow fibrin on an inflamed and swollen mucosa. It differs from necrotizing ulcerative gingivitis in that acute herpetic gingivostomatitis is a viral infection while necrotizing ulcerative gingivitis has other causes.