This is the second of a series of three papers dealing with mental deterioration in epilepsy. Comparison was made of the mental state of 449 "symptomatic" and 1456 "essential" epileptics. Twenty-six per cent of the symptomatic and 10 per cent of the essential group showed definite deterioration, although the former group had experienced fewer seizures. The elimination of patients who were mentally deficient at birth decreased the disparity to 12 and 6 per cent respectively. With respect to the age of patients at the onset of seizures, serious deterioration was more manifest in the symptomatic group in all ages, but the difference was greatest if seizures began in adult life. With respect to the duration of epilepsy, again deterioration was more marked in the symptomatic group in all periods, but the difference was greatest if the epilepsy had just begun. In the symptomatic group deterioration was more often present before seizures began.Patients whose mentality improved while using anticonvulsant drugs numbered for phenobarbital 30 per cent, for bromides 26 per cent, and for patent medicines 13 per cent. Improvement of seizures was noted, respectively, in 65, 53 and 40 per cent of patients reporting the use of these drugs.The psychological causes of pseudodeterioration are important but could not be evaluated in this study.Abstract Teaser