A 29-year-old male was diagnosed with ileocolic Crohn's disease (CD) approximately 2 years ago. Adalimumab was prescribed as CD remission induction therapy. Three months after beginning adalimumab, watery diarrhea and lower abdominal pain developed. He was admitted under a diagnosis of CD exacerbation. Despite fasting and antibiotic treatment, symptoms of acute panperitonitis appeared. He was diagnosed as acute appendicitis and we performed emergency surgery for peritoneal drainage and ileocecal resection on the fifth hospital day. We diagnosed periappendicitis based on the operative findings. This is the first report of periappendicitis with CD during adalimumab treatment.