This investigation was undertaken to determine the mental status of children with convulsive disorder and to investigate the possible relation of retardation to other factors. Children (269) with a diagnosis of convulsive disorder were rated as to mental retardation in 3 groups: (1) retarded, (2) dull-normal, (3) average or better. The group as a whole showed a larger incidence of retardation (37%) than a general normal group (about 10%). The percentage retardation is greater in those cases of convulsive disorders diagnosed as definitely symptomatic (73%) than in those classified as idiopathic (22%). The younger children in the group showed a greater incidence of retardation than the older children (53%, 0-5 years; 24%, 5-10 years; 20%, 10-15 years). Incidence of retardation was greater in those cases with more frequent convulsive attacks than in the cases with less frequent attacks. No relation was found between the incidence of retardation and the diagnostic classification of petit and grand mal nor between retardation and duration of the disease. Patients whose eeg showed well-recognized dysrhythmia and definite types of dysrhythmia had an increase of incidence of mental retardation as compared to those with normal tracings or patients whose tracings were very slightly distrubed. In patients with symptomatic convulsive disorder, the incidence of retardation was high regardless of eeg findings. Of the patients with convulsive disorder, 12.4% had normal eeg tracing. On basis of the findings in this study, no specific type of eeg tracing appeared characteristic of any one clinical type of convulsive disorder.