The report, based on visits to the central African nation by the group in December, documents the use of fear, intimidation and imprisonment against the opponents of President Paul Biya.
"It's time to put an end to such blatant violations of human rights," said Godfrey Byaruhanga, AI's central Africa researcher.
Prisons in Cameroon are grossly overcrowded, AI reported. The human rights group found 7,000 inmates in two prisons with a combined capacity of 1,500. Inmates at one prison eat only meal a day.
Lesbian, gay, transgender and intersex (LGBTI) people in custody are forced to undergo anal examinations to determine if they have had same-sex relationships, which are illegal in Cameroon.
He added that lawyers defending LGBTI inmates have been threatened, as have their children.
In their December visit, AI delegates said human rights violations they reported to Cameroon officials in 2010 were continuing.
The government claims it enforces the laws, but "has little to show for it on the ground," Byaruhanga said.