Taura syndrome (TS) is an economically important disease of Penaeus vannamei (Crustacea: Decapoda) that was first recognized in commercial penaeid shrimp farms located near the mouth of the Taura River in the Gulf of Guayaquil, Ecuador, in June 1992. The syndrome is now known from shrimp farms throughout the Gulf of Guayaquil, as well as from single or multiple farm sites in Peru, Colombia, Honduras, and Oahu, Hawaii, USA. Both toxic and infectious etiologies for TS have been proposed, but TS appears to have a viral etiology due to a previously unrecognized agent now called Taura syndrome virus or TSV. The disease has peracute and recovery (or chronic) phases, which are grossly distinguishable. Peracute episodes of TS are the most common manifestation of TS and occur in juvenile shrimp (of 0.1 to 5.0 g) within 14 to 40 d of stocking into grow-out ponds or tanks. Gross signs displayed by moribund shrimp with peracute TS include expansion of the red chromatophores giving the affected shrimp a pale reddish coloration and making the tail fan and pleopods distinctly red. Peracutely affected animals usually die during the process of molting. The purpose of the present paper is to provide a definition of TS (based primarily on gross signs and histopathology supported by electron microscopy) as a basis for future studies on the disease.