Preliminary reliability and validity data are reported on a new, brief measure of psychiatric symptomatology. The Symptom Assessment-45 Questionnaire (SA-45) is a 45-item, patient self-report symptom inventory derived from the original Symptom Checklist-90-R (SCL-90), using cluster analytic methods. The SA-45 consists of nine 5-item scales assessing each of the same symptom domains as its parent instrument with no item overlap across domains. The vast majority of the internal consistency reliabilities for the SA-45's nine scales were in the .70s and .80s across different age and patient status samples. As expected, both adolescent and adult patient samples generally differed significantly from nonpatient control samples, and patients at treatment follow-up differed significantly from patients at intake. Moreover, depressed patients with and without psychotic features differed significantly on three scales. A cluster analysis generally supported the nine-scale structure of the inventory, but it failed to consistently support the distinction between the Paranoid Ideation and Interpersonal Sensitivity scales. Limitations to the study are noted, but overall, the initial findings support the use of the SA45 in clinical settings. Suggestions for needed future research are presented.