Environmental stress cracking of amorphous poly(ethylene terephthalate) in aqueous sodium hydroxide was studied by using a fracture mechanics approach. Compact tension specimens were machined from injection-molded plaques and used to determine creep crack growth rate as a function of applied stress intensity factor. The effects of caustic concentration and polymer molecular weight on creep crack growth behaviour were determined. Fractographic analysis of the fracture surfaces showed that crack growth proceeded by the formation of novel discontinuous growth bands. The structure and mechanism of formation of these bands are discussed.