A high percentage of psychiatrists (51%) did not return the questionnaire. A likely bias is that those psychiatrists treating patients with a gender identity disorder as a symptom of other psychiatric illnesses completed the questionnaire.

In total, 584 patients were reported by 142 respondent psychiatrists, many working in the same clinical centers or areas. Patients may have been counted more than once by the different respondents. Our gender clinic treats over 95% of the Dutch gender-dysphoric patients. On the basis of our information on the number of patients consulting a psychiatrist outside our clinic, the number of 584 patients seems unrealistically high unless proven otherwise.

Psychiatric comorbidity must be assessed reliably by means of validated research instruments and not by the clinical impression or recollection of responders.

The validity of the conclusions would have been strengthened had the researchers also approached psychologists or general practitioners, who refer the vast majority of patients.

Patients seen by the psychiatrists in our center are not representative of the average gender-dysphoric patient. Obviously, patients with psychiatric disorders will be most likely to consult a psychiatrist. Therefore, external validity is limited and does not warrant the generalizations the authors made +(1).

The patient study group, not having been chosen randomly from the whole population of transsexuals, was biased. This survey cannot make valid inferences beyond the specific group that was surveyed.