Corruption is overshadowing natural disasters and disease as the scourge of poor countries.
An estimated $1tn a year is being taken out of poor countries and millions of lives are lost because of corruption, according to campaigners.
A report by the US-based anti-poverty organisation One says much of the progress made over the past two decades in tackling extreme poverty has been put at risk by corruption and crime.
Corrupt activities include the use of phantom firms and money laundering.
The report blames corruption for 3.6 million deaths every year.
If action were taken to end secrecy that allows corruption to thrive - and if the recovered revenues were invested in health - the group calculates that many deaths could be prevented in low-income countries.
One describes its findings as a "trillion dollar scandal".
"Corruption inhibits private investment, reduces economic growth, increases the cost of doing business and can lead to political instability," the report says.
"But in developing countries, corruption is a killer. When governments are deprived of their own resources to invest in health care, food security or essential infrastructure, it costs lives and the biggest toll is on children."
The report says that if corruption was eradicated in sub-Saharan Africa:
Education would be provided to an additional 10 million children per year
Money would be available to pay for an additional 500,000 primary school teachers
Antiretroviral drugs for more than 11 million people with HIV/Aids would be provided
One is urging G-20 leaders meeting in Australia in November to take various measures to tackle the problem including making information public about who owns companies and trusts to prevent them being used to launder money and conceal the identity of criminals.
It is advocating the introduction of mandatory reporting laws for the oil, gas and mining sectors so that countries' natural resources "are not effectively stolen from the people living above them".
It is recommending action against tax evaders "so that developing countries have the information they need to collect the taxes they are due" and more open government so that people can hold authorities accountable for the delivery of essential services.