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.Une etude retrospective d'une serie de cas fut menee au departement d'urgence d'un hopital universitaire recevant 100 000 malades par annee afin d'identifier l'incidence et les facteurs associes aux diagnostics errones d'appendicite chez des femmes non enceintes agees entre 15 et 45 ans. Cent-soixante-quatorze femmes non enceintes presentant un diagnostic pathologique d'appendicite furent identifiees. Les symptomes cliniques furent alors compares entre ceux des malades chez qui le diagnostic etait errone (vues 10 jours plus tot et incorrectement diagnostiquees) et ceux des malades chez qui le diagnostic initial etait exact. Les resultats demontrerent que dans 33% des cas d'appendicite, le diagnostic initial etait errone. Les diagnostics les plus courants etaient la salpingite aigue, la gastroenterite et les infections urinaires. Dans les cas de diagnostic errone, les malades presentaient plus souvent une douleur et une sensibilite diffuse et bilaterale dans le bas-ventre, de la douleur a la mobilisation du col uterin et une sensibilite annexielle du cote droit. Egalement, chez ces malades, la douleur et la sensibilite a la palpation au niveau de la fosse iliaque droite et les signes peritoneaux etaient moins frequents. De plus, le diagnostic errone etait associe a une plus grande incidence de perforation, de formation d'abces et a une augmentation de la duree totale d'hospitalisation. En conclusion, l'incidence du diagnostic errone d'appendicite chez les femmes en age de procreer est elevee. Dans ces cas, les symptomes et les signes a l'examen physique sont moins typiques et la presence d'anomalies au niveau pelvien est plus frequente que chez les femmes diagnostiquees correctement. Les medecins d'urgence doivent etre conscients que le diagnostic errone d'appendicite est associe a des signes et symptomes atypiques chez des femmes non enceintes en age de procreer.