Professor Lord Robert Winston has received "very unpleasant" online abuse for speaking about the "horrendous" results of 'sex-change' surgery.
Lord Winston, emeritus professor of fertility studies at Imperial College London, warned of the dangers of a "blunderbuss" approach by doctors who are promoting radical surgery.
He made his comments on BBC Radio 4's Today program.
In a tweet, Lord Winston hit back at his online critics for ignoring the evidence.
'High Complication Rates'
He told The Sunday Times that he was "surprised by the amount of vituperation" he received online.
Lord Winston added that the medical literature "shows very clearly there are high complication rates" for genital reconstruction surgery.
And in an article for the Mail on Sunday titled 'Trolls called me homophobic ... but we have to be more cautious', he said that he has been "virulently criticized" by some transsexual activists.
"It is disturbing to be called bigoted and homophobic."
He also warned against "embarking on complex and, mostly, irreversible treatments involving young patients."
"Should we treat young children, perhaps by the age of 9before the onset of puberty, or adolescents who are increasingly unhappy about their gender?
"A 9-year-old who is too young to think in an adult way is at risk. Committing them to hormone therapy which will delay puberty may have undesirable and irreversible long-term effects."
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