Although there is evidence that childhood perfectionistic traits predate the onset of eating disorders, few studies to date have examined the prevalence and clinical correlates of these traits in patients with anorexia nervosa (AN) and their unaffected sisters. The aim of this work was to study the prevalence of childhood obsessive–compulsive traits in patients with lifetime AN, their unaffected sisters and healthy women. A total of 116 AN patients, 32 healthy sisters and 119 controls were assessed by the EATATE Interview to assess traits such as perfectionism, inflexibility, rule‐bound traits, drive for order and symmetry, and excessive doubt and cautiousness. Both self‐report and maternal reports were collected. AN patients reported more childhood obsessive–compulsive traits than their healthy sisters and controls. In contrast, no differences between healthy controls and unaffected sisters emerged. In patients with AN, a dose–response relationship was found between the number of childhood obsessive–compulsive traits and psychopathology, including body image distortion, thus indicating that these traits are an important feature to be considered in assessing and treating eating disorders. Copyright © 2014 John Wiley & Sons, Ltd and Eating Disorders Association.