The only restrictions on dual nationals who are U.S. citizens are that nonimmigrant visas cannot be issued to U.S. citizens and they must enter the U.S. with a U.S. passport.

The following is a partial list indicating which countries recognize dual citizenship. The list is based primarily on a survey of every country in the world . The question presented was "If a citizen of (the country in question) acquires U.S. citizenship, does he or she retain or lose (the country in question's) citizenship? In the list below, "Retain" means that the individual DOES NOT lose his or her prior citizenship upon naturalizing in the U.S. "Lose" means that the individual DOES lose his or her prior citizenship. Where possible, the list in annotated to provide additional relevant information.

If a country is not listed, it either did not respond to the survey or there was no information otherwise available.
ALBANIA (Retain)
ANTIGUA AND BARBUDA (Retain)
ARGENTINA (Retain)
AUSTRALIA (Lose) if the individual acquires another citizenship after reaching 18 years of age.
AUSTRIA (Lose)
AZERBAIJAN (Lose)
BAHRAIN (Lose)
BARBADOS (Retain)
BELGIUM (Lose)
BELIZE (Retain)
BENIN (Retain)
BOLIVIA (Lose)
BRAZIL (Retain) the individual should declare acquisition of U.S. Citizenship at a Brazilian mission or consulate
BRUNEI (Lose)
BURKINA FASO (Retain)
CAMBODIA (Retain)
CANADA (Retain)
CHILI (Lose)
CHINA PEOPLE'S REPUBLIC (LOSE)
COLOMBIA (Retain)
COSTA RICA (Retain) effective June 27, 1995
CROATIA (Retain) the individual must follow specific procedures to renounce
CZECH REPUBLIC (Lose) except if the individual became a US Citizen between September 17, 1938 and May 7, 1957 pursuant to a treaty between Czechoslovakia and the United States
DEMARK (Lose)
DOMINICA (Retain)
DOMINICAN REPUBLIC (Retain)
ECUADOR (Retain)
EL SALVADOR (Retain)
ESTONIA (Retain) 1940 to 1992, as formal release was required (Lose) 1992 to present
FINLAND (Lose)
FRANCE (Retain)
GERMANY (Lose)
GHANA (Retain)
GREECE (Retain)
GRENADA (Retain)
GUATEMALA (Retain)
HONDURAS (Lose)
HUNGARY (Retain) unless it is renounced by a declaration not given in criminal proceedings, and no tax issues apply
ICELAND (Lose)
INDIA (Lose)
IRAN (Retain)
IRELAND (Retain)
ISRAEL (Retain)
ITALY (Lose)
JAPAN (Lose)
KOREA (Lose)
KUWAIT (Lose)
KYRGYZ REPUBLIC (Lose)
LATVIA (Retain)
LESOTHO (Retain)
LIECHTENSTEIN (Retain) but will have diminished rights and protections
LUXEMBOURG (Lose)
MALAWI (Lose)
MALAYSIA (Lose)
MALTA (Retain)
MEXICO (Lose)
MONACO (Lose)
MOROCCO (Retain)
NAMIBIA (Retain)
NEPAL (Lose)
NETHERLANDS (Lose)
NEW ZEALAND (Retain)
NICARAGUA (Lose)
NIGERIA (Retain)
NORWAY (Lose)
PAKISTAN (Lose)
PANAMA (Retain)
PAPUA NEW GUINEA (Lose)
PERU (Retain)
PHILIPPINES (Lose)
POLAND (Retain)
PORTUGAL (Retain)
RUSSIA (Retain) the individual's acquisition of another citizenship will usually not be acknoledged)
RWANDA (Lose)
ST. CHRISTOPHER AND NEVIS (Retain)
ST. LUCIA (Retain)
SAUDI ARABIA (Lose)
SINGAPORE (Lose)
SLOVAK REPUBLIC (Lose) except if the individual became a US Citizen between September 17, 1938 and May 7, 1957 pursuant to a treaty between Czechoslovakia and the United States
SLOVENIA (Retain)
SOUTH AFRICA (Lose) an individual loses citizenship upon becoming a US Citizen; however, citizenship may be retained upon request prior to becoming a US Citizen, or by subsequent application, if the individual was unaware of the loss
SPAIN (Lose)
SRI LANKA (Retain)
SWAZILAND (Lose)
SWEDEN (Lose)
SWITZERLAND (Retain)
TONGA (Lose)
TURKEY (Retain)

UGANDA (Lose)

UNITED KINGDOM (Retain)
URUGUAY (Retain)

VENEZUELA (Lose)
ZIMBABWE (Lose)

How To apply for US Citizenship