In the present investigation verbal statements of certainty, or confidence in the performance of immediate recall and recognition, were related to the neurotic/schizophrenic dichotomy and, within the neurotic group, to personality questionnaires of rigidity, extreme response set, extraversion and neuroticism. The aim was to find pointers to conditions favourable for the investigation of individual differences in certainty and to assess the relative validity of a number of independent personality criteria. Statements of certainty analysed are derived from an immediate recall experiment, the results of which have already been reported (6). An analysis of the interaction between certainty and other measures derived from the same experiment is to be presented at a later date.