Almost one in three deaths in South Africa are caused by Aids making it the leading killer, according to research.
In two provinces, the figure is as high as 40%, says an unreleased report by South Africa's Medical Research Council.
Research was based on the study of death statistics for the year 2000.
A researcher admitted that the report relied partly on estimations, since Aids-related deaths are not always identified on death certificates.
South African media have obtained the document, but the government had declined to comment before the report is released officially.
"HIV/Aids is the leading cause of death and premature mortality for all provinces," the document states.
"The high death rates due to HIV/Aids highlight the urgency to accelerate the implementation of the comprehensive plan for the treatment and prevention of HIV and Aids," the report argues.
The MRC report is the first to include a provincial breakdown of Aids-related deaths.
In KwaZulu-Natal province, 41.5 % of deaths are attributable to Aids, followed by Mpumalanga with 40.7 percent, the report says.
In Gauteng, South Africa's economic heartland, Aids accounts for 32.5% of deaths, according to the report.
Campaigners say the government should do more to halt the epidemic
Lead researcher Debbie Bradshaw told the South African Press Association that the findings were based on various data sets, including official cause of death figures.
It also considered changing patterns in death ratios, and identified nine death-causing conditions that showed a distinct change.
"There is some uncertainty, because we don't have the truth at hand to compare it against," Dr Bradshaw said. "But we don't think we are over- or understating the picture. These are the best estimates we can come up with."
More than five million South Africans are HIV positive and the government has been criticised by Aids campaigners for being slow to roll out anti-retroviral drugs to all.