The procedure is being performed even on first-time, non-violent offenders, such as exhibitionists, its investigation revealed.
Prisoners have to request castration under Czech law, but many fear they will be jailed for life if they do not, the investigation found.
"In practically all the cases, these patients indicated that their application was at least partially instigated by fear of long-term detention," the report said.
"Some patients claimed that the treating sexologist had explicitly told them that surgical castration was the only available option to them and that refusal would mean lifelong detention."
And it warned that some "significantly" mentally retarded people had been castrated. "In at least five cases, legally incapacitated offenders were surgically castrated," the report said. "In all of these instances, the court-appointed guardian had signed the consent form; in two cases, the guardians were mayors."
The investigators found only two convicts who had spontaneously volunteered for castration, while others they interviewed said mental health staff specializing in sexuality had recommended it.
"The other patients interviewed indicated that the treating sexologist had suggested surgical castration, in several cases within a week of the patient's admission to hospital," the report said.
"Some of the sexologists interviewed by the delegation themselves affirmed that for certain patients there was no alternative treatment to surgical castration."