Serious levels of corruption in the public sector plague more than two-thirds of the world's nations and are undermining attempts to eradicate poverty, Transparency International said.
At the other end of the scale, Iceland was the least corrupt country.
Berlin-based Transparency International said on Tuesday more than two-thirds of the 159 nations on the list scored less than five out of 10, indicating serious levels of corruption.
Peter Eigen, chairman of Transparency International, said corruption among public officials was worsening poverty in many developing countries.
"The two scourges feed off each other, locking their populations in a cycle of misery," Eigen said. "Corruption must be vigorously addressed if aid is to make a real difference in freeing people from poverty."
To form its annual corruption index, Transparency International asks businesses, workers, academics and public officials about how countries they live in or do business with are perceived.
Bangladesh and Chad both scored 1.7%, while the least corrupt country, Iceland, scored 9.7%.
"We see a low score as a sign of structural health failure and a sign that action needs to be taken," said Transparency International chief executive David Nussbaum.
Following are the least and the most corrupt countries in the index, with their scores out of 10. The higher the score, the lower the perceived level of corruption.
1. Iceland 9.7
2. Finland 9.6
3. New Zealand 9.6
4. Denmark 9.5
5. Singapore 9.4
6. Sweden 9.2
7. Switzerland 9.1
8. Norway 8.9
9. Australia 8.8
10. Austria 8.7
144. Democratic Republic
of Congo 2.1
145. Kenya 2.1
146. Pakistan 2.1
147. Paraguay 2.1
148. Somalia 2.1
149. Sudan 2.1
150. Tajikistan 2.1
151. Angola 2.0
152. Ivory Coast 1.9
153. Equatorial Guinea 1.9
154. Nigeria 1.9
155. Haiti 1.8
156. Myanmar 1.8
157. Turkmenistan 1.8
158. Bangladesh 1.7
159. Chad 1.7
Nussbaum said many developing countries needed to reform their public sectors to ensure that United Nations aid programmes reached the poverty-stricken populations they were intended to help.
The UN has a goal of halving extreme poverty by 2015. "We need to work with countries to create programmes all believe will be effective. The donors need to be confident that the aid will go to the right place," Nussbaum said.
"Recipient-led reform is very important."
Turkmenistan, Myanmar, Haiti, Nigeria, Equatorial Guinea, the Ivory Coast and Angola joined Bangladesh and Chad as the most corrupt countries, according to the organisation's report.
After Iceland, the least corrupt were Finland, New Zealand, Denmark, Singapore, Sweden, Switzerland, Norway, Australia and Austria.
The watchdog said Costa Rica, Gabon, Nepal, Papua New Guinea, Russia, Seychelles, Sri Lanka, Suriname, Trinidad and Tobago and Uruguay all recorded an increase in perceived corruption from last year's survey.
Conversely, Estonia, France, Hong Kong, Japan, Jordan, Kazakhstan, Nigeria, Qatar, Taiwan and Turkey all showed a decline in perceptions of corruption.
In Dhaka, the Bangladesh government blamed the previous administration for being placed at the top of the corruption list for the fifth year in a row.
Last year, Bangladesh shared its position with Haiti although the government rejected the watchdog's methodology, saying the index should be based on facts, not perceptions.
Reacting to the 2005 index, Bangladesh Information Minister Shamsul Islam said there had been a steady reduction in corruption since the current government took power.
The four-party coalition government led by Prime Minister Khaleda Zia's Bangladesh Nationalist Party was elected in 2001, ousting Shaikh Hasina Wajed's Awami League government. The Awami League is now the main opposition.
Islam cited the country's new Anti Corruption Commission (ACC) as proof of the government's commitment to curbing the problem. "The ACC has started functioning and soon it will have positive effect," he added.