Temperature effects on the photoluminescence spectrum, phosphorescence lifetime and phosphorescence intensity of poly(ethylene terephthalate) have been investigated in the range -185 to +30 degreesC. Bath the fluorescence and phosphorescence emission spectra are composed of a monomeric-like component and a red-shifted emission attributed to the formation of ground state dimers. Monomeric emissions are enhanced at low temperature. The transient phosphorescence signals at excitation switch-on and switch-off are clearly not exponential, but could be suitably fitted to a stretched-exponential function. The temperature dependence of the related parameters is discussed. The kinetic analyses of temperature effects on steady-state phosphorescence indicated that phosphorescence quenching is controlled by oxygen diffusion. A correlation between the phosphorescence decay and the secondary relaxation of PET as probed by dielectric spectroscopy has been established.