Questionnaire-based dimensional measures are often employed in epidemiological studies to predict the presence of psychiatric disorders. The present study sought to determine how accurately 4 dimensional mental health measures, the 12-item General Health Questionnaire (GHQ-12), Neuroticism (EPQ-N), the high positive affect and anxious arousal scales from the Mood and Anxiety Symptoms Questionnaire (MASQ-HPA and MASQ-AA) and a composite of all 4, predicted psychiatric caseness as diagnosed by the University of Michigan Composite International Diagnostic Interview (UM-CIDI). Community subjects were recruited through general practitioners; those who agreed to participate were sent a questionnaire containing the above measures. Subsequently, the UM-CIDI was administered by telephone to 469 subjects consisting of sibling pairs who scored most discordantly or concordantly on a composite index of the 4 measures. Logistic Regression and Receiver Operating Characteristic (ROC) curve analyses were carried out to assess the predictive accuracy of the dimensional measures on UM-CIDI diagnosis. A total of 179 subjects, 62 men and 117 women with an average age of 42 years, were diagnosed with at least one of the following psychiatric disorders: depression, dysthymia, generalized anxiety disorder (GAD), social phobia, agoraphobia and panic attack. The six disorders showed high comorbidity. EPQ-N and the Composite Index were found to be very strong and accurate predictors of psychiatric caseness; they were however unable to differentiate between specific disorders. The results from the present study therefore validated the four mental health measures as being predictive of psychiatric caseness.