Chalong Police Station inspector Pol Capt Thada Sodarat said both the American and the ladyboy died at the scene, close to the Rawai Public Park.
He said the American, Theodore Paul Roe, was riding on one motorbike, and two ladyboys were riding together on another bike.
It is not clear yet what happened, nor even whether the bikes were going in the same or opposite directions, but the two bikes apparently collided, and both drivers – Mr Roe and Saknarin Wilarm from Mahasarakam Province – died at the scene.
Friends said that they understood the duo pulled out of a side road right in front Mr Roe.
The ladyboy pillion passenger was injured and taken to Vachira Hospital Phuket.
Capt Thada said he was unable to provide more information on the crash until the investigation had been completed.