A two-year-old boy has been left infertile after surgeons operated on the wrong testicle, his family says.
The boy was admitted to Bristol Royal Hospital for Children earlier in the week to treat an undescended testicle.
He had one healthy testicle and one that did not function. His father said surgeons operated on the wrong one by mistake and have "castrated him".
University Hospitals Bristol has apologised and said it has launched a serious incident investigation.
The boy's father, whose name has not been used to protect his son's identity, said his son's undescended testicle was discovered during a routine check up.
The toddler boy was referred to a specialist and on Monday he was booked in for an operation at the Bristol Royal Hospital for Children.
'No more tears'
The family said they were told it was "just a minimal operation" with "minimal risk" and it would be over in around 30 minutes
"We were waiting and waiting," his father said.
"After two and a half hours the manager, surgeons and consultants they came and I knew something was not right.
"Me and my wife started panicking, they called us into the office and told us things didn't go right and the operation wasn't a success."
The couple said they were told a surgeon had mistakenly inserted a camera "into the wrong side" and now their son's healthy testicle would "never work".
"I was very distressed, it was an awful disaster for a simple operation they destroyed everything and they ruined my son," his father said.
"They castrated him and now my son's future life has dramatically changed."
The boy's mother said it was "absolutely horrible" what the surgeons had done.
"They broke my heart and they basically destroyed his future," she said.
"I can't find the words to explain how I'm feeling - there are no words. Even tears, I have no more tears.
"We just hope for a miracle, this is what we hope."
In a statement, University Hospitals Bristol apologised saying it was "deeply sorry".
"As soon as our staff members realised what had happened, they met with the family, told them what happened, and apologised again at that point," a spokesperson said.
"I would like to re-iterate that we take patient safety extremely seriously here and also the quality of our clinical care.
"As a result, a serious incident investigation has been launched. We will keep the family informed and involved in this process."
It is estimated that about one in 25 boys are born with undescended testicles, according to NHS online.
Around one in 100 boys has testicles that stay undescended unless treated.
The NHS said the "relatively straightforward" operation to move testicles into the correct position in the scrotum has a "good success rate".