Background: The present study determined the psychiatric comorbidity of Axes I and II in a sample of subjects with eating disorders (EDs). The objective was to investigate associations between comorbidity and current and past treatment. Methods: In a sample of 248 women (77 anorexia nervosa, 137 bulimia nervosa, 34 eating disorders not otherwise specified), psychiatric comorbidity of Axes I and II was determined with the Structured Clinical Interview of DSM-IV. Current and past treatment since ED onset were also assessed. Results: High levels of psychiatric comorbidity were found in the total sample (71% Axis I and 68% Axis II). Only 17% of cases had no psychiatric comorbidity. Anxiety (52%) and affective disorders (50%) were the most common Axis I diagnoses. Personality disorders of Clusters C (52%) and B (23%) were most common for Axis II. Twenty-one percent of participants who were not in treatment at the time had a history of inpatient treatment, and an additional 59% had a history of outpatient treatment. Thirty-eight percent of participants currently in outpatient treatment had a history of inpatient treatment. Participants with multiple comorbidity (Axes I and II) had the highest proportion of cases who had been treated by health professionals. Higher levels of comorbidity were associated with experiences in more intense treatment settings (ranging from no treatment to inpatient treatment). Conclusions: ED subjects with greater comorbidity require more treatment encounters and more intense treatment settings. The association between comorbidity and treatment experiences may represent a bias in the assessment of comorbidity when samples with heterogeneous treatment history are recruited.