Cognitive reactivity to the experimental induction of sad mood has been found to predict relapse in recovered depressed patients. The present report describes the development and test of a questionnaire that aims to measure cognitive reactivity independently from a mood induction procedure. The Leiden Index of Depression Sensitivity (LEIDS) was filled out by 198 participants. After Principal Components Analysis, 26 items were retained, which comprised four factors with good psychometric properties: Negative Self-Evaluation; Acceptance/Coping; Indifference; and Harm Avoidance. In a sample of 48 college students, LEIDS scores--particularly Negative Self-Evaluation and Harm Avoidance--were rather strong predictors of cognitive reactivity in a mood induction procedure. In contrast, baseline depression and baseline cognitive dysfunction did not predict cognitive reactivity. It is concluded that the LEIDS is a promising measure of cognitive reactivity, and that clinical studies need to be carried out to test its ability to predict relapse of depression.