Linked in the past to sex crimes in East Timor, and prostitution in Cambodia and Kosovo, UN peacekeepers have now been accused of sexually abusing the very population they were deployed to protect in Congo.
And while the 150 allegations of rape, pedophelia and solicitation in Congo may be the UN's worst sex scandal in years, chronic problems almost guarantee that few of the suspects will face serious punishment.
The problem is simple: The UN often implores nations to discipline their peacekeepers, but it has little power to enforce the rules. And when nations are reluctant anyway to contribute soldiers for dangerous missions like Congo, it's tough to turn the tables and shame them publicly.
"The UN goes around trying to cajole countries to provide peacekeepers," said Edward Luck, a professor at Columbia University's School of International and Public Affairs. "They're having a hard time getting any member states to respond, and that doesn't give the UN a great deal of leverage in these kinds of situations."
While thousands of UN peacekeepers have served without incident, some have been accused of smuggling weapons and exotic animals, selling fuel on the black market, vandalizing airplanes, and standing by while mobs looted storefronts -- if they didn't join in the chaos themselves.
Other times their inaction led to even more grievous crimes, as when Dutch peacekeepers under a UN mandate didn't stop Bosnian troops in the enclave of Srebrenica from loading Muslim men onto buses and taking them away to be killed.
That failure led the entire Dutch government to resign. It brought expressions of remorse at the UN, but no firings.
In the case of Congo, the accusations seem as bad as anything the UN has ever seen. Women and children have reportedly been raped, and there is said to be video and photographic evidence of crimes.
Similar allegations have been directed at UN peacekeepers and officials in East Timor. And, in Cambodia and Kosovo, local officials and human rights group charge that the presence of UN forces has been linked to an increase in trafficking of women and a sharp rise in prostitution.
In a new embarrassment, the UN confirmed Tuesday that a UN auditor in the Congolese capital, Kinshasa, had been accused of hiring a prostitute. He comes from the agency that is investigating the latest claims, but isn't taking part in the probe.
The Congo allegations come at a particularly bad time for the UN and its Secretary-General Kofi Annan.
UN officials have been accused of allowing corruption under Iraq's oil-for-food program. The refugee chief was accused of sexual harassment and cleared by Annan, which angered UN staff. The UN's top investigator allegedly recruited and promoted staff based on their ethnicity, but was also cleared by Annan.
"The last 18 months have been one of the worst years and a half for the United Nations of any similar period that I can remember," said Jonathan Tepperman, editor at Foreign Affairs magazine.
Jane Holl Lute, Assistant Secretary-General for Peacekeeping Operations, warned that the UN may even "generate new policies" to crack down on sex abuse, though she said it's too early to say what those policies would be.
Lute said it's possible sex abuses had gotten worse because there are far more peacekeeping missions than there once were. But right now, it must focus on prevention, with its ability to punish so limited.