This paper describes a questionnaire measure of self-reported failures in perception, memory, and motor function. Responses to all questions tend to be positively correlated, and the whole questionnaire correlates with other recent measures of self-reported deficit in memory, absent-mindedness, or slips of action. The questionnaire is however only weakly correlated with indices of social desirability set or of neuroticism. It is significantly correlated with ratings of the respondent by his or her spouse, and accordingly does have some external significance rather than purely private opinion of the self. The score is reasonably stable over long periods, to about the same extent as traditional measures of trait rather than state. Furthermore, it has not thus far been found to change in persons exposed to life-stresses. However, it does frequently correlate with the number of current psychiatric symptoms reported by the same person on the MHQ; and in one study it has been found that CFQ predicts subsequent MHQ in persons who work at a stressful job in the interval. It does not do so in those who work in a less stressful environment. The most plausible view is that cognitive failure makes a person vulnerable to showing bad effects of stress, rather than itself resulting from stress.