A retrospective case series was conducted at a teaching hospital with an emergency department (ED) census of 100,000 patients per year to identify the incidence of, and factors associated with, the misdiagnosis of appendicitis in nonpregnant women aged 15 to 45 years. There were 174 nonpregnant women identified with a pathologic diagnosis of appendicitis. Clinical features were then compared between patients misdiagnosed (seen in prior 10 days and given an incorrect diagnosis) and those who were initially diagnosed correctly. The results showed that 33% of the women with appendicitis were initially misdiagnosed. The most common misdiagnoses included pelvic inflammatory disease, gastroenteritis, and urinary infections. Misdiagnosed women more frequently exhibited diffuse and bilateral lower abdominal pain and tenderness, cervical motion, and right adnexal tenderness. Misdiagnosed women also had a lower incidence of right lower quadrant pain and tenderness, and peritoneal signs. In addition, misdiagnosis was associated with an increased incidence of perforation, abscess formation, and an increase in the total length of hospitalization. In conclusion, the incidence of misdiagnosis of appendicitis in women of childbearing age is high. Women who are misdiagnosed have less typical symptoms and physical findings and more frequent abnormal pelvic findings than those who are diagnosed correctly. Emergency physicians should be aware that atypical signs and symptoms are associated with misdiagnosed appendicitis in nonpregnant women of childbearing age.