Etienne Swanepoel, 35, had begun what he thought was to be a hysterectomy on the cat, called Fat Cat, in October 1991 at his clinic in Stanstead Abbots, Hertfordshire, when the nurse assisting him spotted it was a male.
But Mr Swanepoel, of Standon, Hertfordshire, did not admit the mistake and charged the cat's owner, Julie Gambell, pounds 207, the disciplinary committee of the Royal College of Veterinary Surgeons was told. He told Mrs Gambell, a secretary, of Ware, Hertfordshire, that Fat Cat was a hermaphrodite.
He was found guilty of disgraceful professional conduct by failing to tell her the cat was male and by charging pounds 207, part of it for the hysterectomy he did not perform.
Counsel to the committee, James Watt, said misconduct did not arise out of the wrong diagnosis but from the dishonesty following discovery of the mistake.
Mrs Gambell told the hearing that Mr Swanepoel had told her Fat Cat was pregnant. When the kittens did not arrive, he X-rayed the cat and pointed to where he thought the dead kittens were. He said an operation was needed.
Angela Crow, the nurse who helped him, said that during the operation she asked if he was sure the cat was female. He laughed and said: 'Well, it better had be.'
On looking at the cat's genital area she realised it was male and had been neutered. Mr Swanepoel became very angry and later falsified the record sheet.
Mr Swanepoel declined to answer the allegations but requested that his name be removed from the register as he no longer wished to practise.