The following information is taken from the U.S. Department of State Website regarding Panama travel visas for American tourists:
Anyone not bearing identification at all times, including tourists from the United States, will be penalized by the Panamanian authorities. U.S. tourists need to provide an original, valid passport at entry in Panama. While in Panama, American tourists should carry either their original passport or an original, valid photo I.D. such as driver’s license with a photocopy of the bio-data page in their U.S. passport and a photocopy of the page in their passport that contains the entry stamp to Panama.
ENTRY / EXIT REQUIREMENTS: U.S. citizens traveling by air to and from Panama must present a valid passport when entering or re-entering the United States. Sea travelers entering Panama must have a valid U.S. passport.
Panamanian law requires that travelers present a passport valid for at least three months. U.S. citizens entering Panama as tourists will be charged $5.00 for a tourist card when they purchase their travel ticket. To obtain a multiple entry visa, please contact the Panamanian embassy or the Panamanian consulate before traveling.
As of April, 2010, U.S. tourists are allowed to stay in Panama for 180 days, without extension. If you want to stay longer, a “change of migratory status visa” should be requested through a Panamanian lawyer before the expiration of the 180 days in country. An initial fee of $250.00 must be paid for the “change of migratory status visa.” Please note that the approval of the change in migratory status falls under the Panamanian Immigration Office’s discretion.
U.S. citizens transiting the Panama Canal as passengers, regardless of their intention to disembark from the ship or not do not need to obtain visas, or pay any fees. If you are piloting a private craft or plane, then you need to have a pre-stamped visa from a Panamanian Embassy or consulate, as do persons crossing into Panama by land.
Minors who are citizens (including dual-citizens) or legal residents of Panama are required to present birth certificates and notarized consent from both parents (in Spanish) in order to exit the country if not accompanied by both parents. This documentation is required at all land, sea, and air ports. Even if minors are not documented as Panamanian citizens and are documented as U.S. citizens, they may be denied departure. If your consent documents are notarized in the United States, they still need to be authenticated in the U.S. with an Apostille stamp.