The warning followed media reports that male teenagers in central Thailand had rushed to have their *****es injected with olive oil or other liquids.
"Injecting olive oil or any liquid into *****es is extremely risky," Chatri Banchuin, chief of the Department of Medical Services, said after his office issued the public warning.
"By the time they know what actually happened, it is too late," he told Reuters.
The practice of injecting liquids -- everything from paraffin to lubricant gel -- has gone on for decades, surgeons say, but their patients are getting younger.
"More and more patients are school age boys, not men in their 30s or 40s like in the past," said urologist Wachira Kochawkarn of Bangkok's Ramathibodi Hospital.
"At my hospital alone, I treat one or two patients a day who have such problems. Imagine the total number across the country?"
The public health warning issued earlier week urged men to be happy with their natural size.
"Sex satisfaction does not depend on ***** size, but it involves love and mutual understanding," the ministry said.