The temperature dependence of intramolecular [2 + 2] photocycloadditions has been studied for two series of cyclohexenones, alpha- and beta-linked, respectively, to a variously substituted olefin moiety via a trimethylene chain. With one exception, the disappearance quantum yield of the starting material decreases sharply in a narrow temperature range to approximately one-half of its initial value. No such sharp temperature effect was observed on the product ratio, which either remains constant or varies monotonically over the entire temperature range. This indicates that the temperature effects on the disappearance rate and on the product distribution refer to two distinct processes. A mechanism rationalizing this behavior is proposed.