The Deputy Health and Disability Commissioner says a counsellor who had sex with a client exploited the woman's extreme vulnerabilities and acted unethically.
Commissioner Tania Thomas said in a decision released on Monday that the counsellor breached aspects of the patient rights code.
The unnamed male counsellor admitted a sexual relationship began between him and the unnamed woman, but says it occurred after counselling had ended in 2006.
The woman said that the counselling sessions had never ended but became a mix of counselling and sex.
Tania Thomas says the woman had been sexually abused by her father and an earlier psychologist, was vulnerable and had trusted and relied on the counsellor.
Ms Thomas says whenever the sex began, it should never have happened.
She says she will not take the matter further, partly because the man is retired and will not be practising again.