The inability to generate oral-verbal expression, despite normal comprehension of speech. This may be associated with brain diseases or mental disorders. Organic mutism may be associated with damage to the frontal lobe; brain stem; thalamus; and cerebellum. Selective mutism is a psychological condition that usually affects children characterized by continuous refusal to speak in social situations by a child who is able and willing to speak to selected persons. Kussmal aphasia refers to mutism in psychosis. (From Fortschr Neurol Psychiatr 1994; 62(9):337-44)