Summary Introduction Sex reassignment surgery is carried out in France with the approval of a multidisciplinary team of psychiatrists, psychologists, endocrinologists and surgeons. The specialists monitor the patient for at least 2 years before any irreversible surgical decision concerning the sexual organs is taken. Objective To understand the reasons for regrets after surgery and to review our psychological and psychiatric assessment tools. Method We present here an exceptional case of an individual who wants to return to his birth sex just days after surgery. The individual concerned was born male and was monitored by the team for a period of 8 years before the decision for surgical intervention was taken. We studied the patient's file in detail including the various consultations he had with the psychiatrist of the transgender unit and with the rest of team. We also analyzed the results of psychological tests and the follow-up questionnaire. Results The use of psychological tests did not shed any light on the high risk of postoperative regret in this case. The elements of differential diagnosis were discussed but the patient was untruthful in his answers. Conclusion The scientific literature shows that the risk of regret is higher among men who have experienced a long heterosexual life, whose request for sex reassignment comes late in life, and who do not receive the support of family and friends. To this conclusion, we might add that the lack of sex life, interruption of the treatment and the absence of gender disorder in childhood seem to be significant criteria for risk of postoperative regret. In addition, in our unit, we have abandoned the use of psychological tests to assess the request of transgender patients.