An increase in life event stress has been shown to occur prior to the onset of a number of psychiatric illnesses. This paper describes the construction of a scale to measure the cause of this increased life event experience. One hundred and five normal adults were asked to judge the extent to which any particular event might have occurred by pure chance, by one's own behaviour or by the behaviour of others. These three perceived causative factors are conceptually distinct and together comprehensive. Scalings on these three perceived causative factors for each of 67 life events were derived. The utility of such a scale is discussed.