The Kenya AIDS Indicator Survey said 57 percent of HIV-positive people said they had never taken an AIDS test while 26 percent said they were HIV negative but later tested positive.
"As many as four out of five HIV-infected persons do not know their status," the report said.
"Nearly two-thirds of Kenyans report never having tested for HIV and are therefore unaware of their status," it added.
National Aids Control Programme chief Ibrahim Mohamed said "sixteen percent did not want to know their test results or were afraid others would know the results."
Another "fourteen percent were unaware of the test for HIV or where to get tested and five percent cited distance to testing (centres) as a major barrier."
Some 1.4 million Kenyan adults are living with the HIV/AIDS.
The survey, carried out between August and December 2007, is the first since 2003. It did not include children.
"We have made notable progress, however HIV/AIDS rates among our families and communities remains unacceptably high and the impact severe," Health Minister Beth Mugo said at the launch of the report.
Around 33 million people worldwide were living with HIV in 2007, two million of whom were children and another two million died of AIDS-related causes, according to a report released Tuesday by the UNAIDS.
However deaths from AIDS-related illnesses fell last year for the second year running mainly due to the widening distribution of drugs, it said.