However, Mr Mayr, a psychologist and author of children's books, has been found guilty of professional misconduct for having a sexual relationship with a patient he was treating for past sexual traumas.

The NSW Civil and Administrative Tribunal detailed a series of transgressions, which included Mr Mayr licking the patient's face during therapy and engaging in "inappropriate sexual contact" at the end of other sessions.

He subsequently had what the tribunal called an "inappropriate sexual relationship" with the patient for almost two years, including having sex with the patient on his desk at his clinic in Penrith.

On another occasion, Mr Mayr performed oral sex on the patient while she was on the clinic's kitchen bench.

The tribunal said Mr Mayr failed to provide appropriate care and treatment by suggesting the patient watch Last Tango in Paris and 1977 French film Bilitis, which one reviewer said: "If released today, its lingering, leery shots of barely developed school girls would no doubt cause a Bill Henson-like backlash."

The tribunal cancelled Mr Mayr's registration to practise psychology for five years.

"The profession needs to be made aware that such behaviour cannot be tolerated by the profession without damage to the good name of the profession of psychology," the tribunal said in its judgment.

The tribunal said Mr Mayr would have been fully aware of a power imbalance a psychologist and a patient in a vulnerable state: "Nevertheless he proceeded to use that imbalance of power to satisfy his own needs."

The tribunal noted that sex between psychologists and patients is prohibited under the Australian Psychological Society's code of ethics.

Mr Mayr first met the patient in 2006 when she brought her preschool age child, who suffered from anxiety, to his St Marys/Penrith Psychological Services clinic.

Four years later, she returned to the clinic with her oldest child who had Asperger's Syndrome before beginning regular therapy sessions with Mr Mayr.

The tribunal said Mr Mayr failed to maintain appropriate professional boundaries with his patient by sharing personal information including extra marital affairs and "past indiscretions with a female patient".

The tribunal said Mr Mayr commented on similarities between the patient and the main character in the children's book he was writing.

Mr Mayr's first book, Ilsa, the funny looking hippopotamus, was published in 2012 and won a "Mom's Choice Award" in 2013, according to his author website.

"Ilsa's innocence and genuineness captivate and unite people of all ages around the world," the website said.

He wrote a second book, Ilsa's waterhole of priceless treasures, and sold Ilsa merchandise.

Meanwhile, the tribunal said Mr Mayr sent emails from mid-2011 to his patient detailing his sexual fantasies and "encouraged her to perform or engage in certain sexual activities".

In one therapy session, the tribunal said Mr Mayr kissed the patient's stomach and breasts and "stated words to the effect of 'I am the type of person who would be in the shower with you and would take a shampoo bottle and put it up your arse'."

Appearing before the tribunal, the patient said Mr Mayr had not explained why his sexual advances, apart from hugging, would be helpful as a method of treatment.

"She did not know whether he helped her but her mental state was such that whatever he wanted her to do she would go along with it," the tribunal said. "After a moments reflection she stated that he did not help her and in fact made her worse."

The tribunal said Mr Mayr lacked insight into his conduct "save as it impacts upon himself and he speaks of 'this one error in judgement' as if his course of conduct over a period of three years could be limited in this way".

Mr Mayr declined to comment but indicated that he would seek to appeal against the decision.

Cameron Stewart, a professor of health, law and ethics at the University of Sydney, said dozens of doctors and psychologists had been struck off for having sex with patients.

"People are unaware of how often this happens," he said.

Professor Stewart said inappropriate sexual relationships particularly occurred with vulnerable patients: "The connection between a health professional and the patient is so strong that it's hard for some health practitioners to differentiate the therapeutic relationship and relationships of affection."