Psychiatric disorders are common in chronic fatigue (CF) and chronic fatigue syndrome (CFS). To determine the usefulness of the General Health Questionnaire (GHQ), a self-report measure of psychological distress, in identifying those with psychiatric illnesses, a structured psychiatric interview and the GHQ were administered to 120 CF and 161 CFS patients seen in a referral clinic. Overall, 87 (35%) patients had a current and 210 (82%) a lifetime psychiatric disorder. Compared to patients without psychiatric disorders, GHQ scores above the threshold (greater than or equal to 12) were more frequent among patients with current (p<0.001) and lifetime (p<0.05) diagnoses; scores among patients with CF and CFS were similar. Longer illness duration, greater fatigue severity, and current psychiatric disorders were significant predictors of the GHQ score. In CF and CFS, the best sensitivity (0.69-0.76) and specificity (0.51-0.62) were achieved for current psychiatric diagnoses using a threshold score of greater than or equal to 12. Thus, patients scoring <12 on the GHQ are significantly less Likely to have a psychiatric disorder. Copyright (C) 1997 Elsevier Science Inc.