Using the Scale for the Assessment of Thought, Language, and Communication (TLC), we examined the frequency of "thought disorder" in 94 normal volunteers and 100 psychiatric patients (25 each suffering from manic disorder, schizoaffective disorder, schizophrenic disorder, disorganized type, and schizophrenic disorder, paranoid type). We observed the manics to have a substantial amount of thought disorder and the normals to have a modest amount, suggesting that thought disorder is probably not pathognomonic of schizophrenia. The patients with affective illness did, however, show a somewhat different pattern of abnormality. In particular, patients with affective psychosis have more prominent positive thought disorder, while the schizophrenic patients tend to have more negative thought disorder. Evaluation of the patients 6 months later indicated that most types of thought disorder remit in the manics, while they persist in the schizophrenics; patients with schizoaffective disorder also tend to improve substantially. The strongest predictor of outcome was the presence of negative thought disorder.