The stability of polyvinyl chloride (PVC) films to UV and visible light was examined. From the linear relationship between the amount of hydrogen chloride evolved and the number of photons absorbed, the dehydrochlorination quantum yield of UV-irradiated PVC was estimated to be 0.011 in a nitrogen atmosphere and 0.015 in pure oxygen. The quantum efficiency is reduced by half by inducing the degradation with the 488 or 514.5 nm radiation of an argon ion laser. The initiation of the PVC photodegradation is assumed to involve an intramolecular energy transfer from excited singlet states of polyenes to the allylic CCl bond. From the lack of any oxygen inhibition effect it is inferred that β-chloropolyenyl radicals have a short lifetime (less than 1 μs) and disappear before being scavenged by oxygen by splitting off chain carrier chlorine radicals.