The main aspects of the geosynclinal and orogenic evolution of the Petchabun foldbelt in Central Thailand are described. This area was previously thought to be deformed by the „Indosinian“ (Triassic) orogeny. The new data show that the main orogenic event in Thailand can be dated: Post Lower Permian — Pre Uppermost Permian. Evidence is given that „Paleotethys“ closed on Thai territory during this orogenic event. The known Upper Triassic deformations in Northern Thailand are supposed to be strictly intracontinental and therefore of minor importance.