85 students and 72 medical and surgical patients, aged between 16 and 24. and 48 mature-aged clerical and executive workers, aged between 29 and 60. Were administered a written version of a scale measuring transient thought disorder, the Eysenck personality questionnaire and the EMBU questionnaire on parental rearing methods. It was found that there were differences between samples on frequency of depersonalisation. and that a majority of the young adult sample had had two or more depersonalisation experiences. Those who had experienced the greater degree of transient thought disorder had had fathers who were more intolerant, unaffectionate and unstimulating, and mothers who were more intolerant, unstim-ulating and rejecting. Transient thought disorder was related significantly to both psychoticism and particularly to neuroticism on the EPQ in the young, but not the mature adult. Sample. It is suggested that it arises as a function of remote and uninvolved parents and is related to uncertainty about identity.