Releasing a report on a study on the topic, Statistics SA on Thursday noted that there had been a change in mortality patterns over the period concerned.
During 1997 to 2001 most deaths resulted from unnatural causes such as injuries, suicides, car accidents and drowning.
Next in line was what it described as ill-defined causes, tuberculosis, HIV/Aids and influenza and pneumonia.
"The proportions of deaths due to unnatural causes has declined during this period while the proportion due to HIV, tuberculoses and influenza and pneumonia has increased."
Stats SA concluded that "where as males experienced the highest mortality attributable to unspecified unnatural causes in the age group 15 to 39, female South Africans in the same age category died primarily as a result of HIV infections".
The study was commissioned after the Medical Research Council released a report last year - conducted with Stats SA - which showed that 40% of deaths of those aged between 15 and 49 in 2000 were due to Aids.
Stats SA later repudiated this finding and questioned the report.
Cabinet then asked Stats SA to do its own study.In a statement issued at the briefing, the Department of Health said the change in patterns of mortality confirmed the need to put the country's anti-aids strategy into effect.