HIV/Aids activists in Kenya have been shocked by the first lady's comments that young people had "no business" using condoms.
This not the first time that Lucy Kibaki has courted controversy
Lucy Kibaki called on students at a school prize-giving to abstain from sex in order to avoid infection with HIV.
Her statement contradicts government policy that promotes condom use.
The BBC's Caroline Karobia says Mrs Kibaki is influential, as she chairs the Organisation of the 40 African First Ladies Against HIV/Aids.
This stance puts her in line with Ugandan first lady Janet Museveni, who backs a campaign for young Ugandans to pledge abstinence until marriage.
"Those who are still in school have no business having access to condoms. Those who are in university and are not married have no business having condoms in their halls of residence," she told schoolgirls in the capital, Nairobi, on Thursday evening.
However, Aids activists say research shows that young people in Kenya are often sexually active from the age of 14.
Elsa Ouko, the national co-ordinator of the Kenya Network of HIV-Positive Teachers, says Mrs Kibaki's remarks come as a shock because in her opinion condom use is the only option.
"Let us be frank, because I think abstinence is not there. If it was there, kids who are 15 years old would not have been giving birth," she told the BBC.
"The truth is that in Kenya even a youth who is 12 years old knows what sex is."
On a visit to a Nairobi boys' secondary school on Friday morning, our correspondent says most pupils interviewed admitted to being sexually active.
Some 1.5m Kenyans have died of Aids or HIV-related diseases since 1984, reports the AFP news agency.
It is not the first time Mrs Kibaki has courted controversy.
Last year, she stormed the offices of the Daily Nation newspaper to complain at coverage of her and slapped a cameraman filming the outburst.