The Kessler 10 Psychological Distress Scale (K10) is a brief 10-item questionnaire designed to measure the level of distress and severity associated with psychological symptoms in population surveys. It is being used widely, including in the World Health Organization World Mental Health Survey, and as a clinical outcome measure, although little information is available about the structure of the measure. The factorial composition of the K10 was examined in a prospective community survey and cross-validated in a separate large community survey. The K10 was found to consist of 4 factors and a 2-factor second-order factor structure. This was stable across the 2 waves of the prospective study and the Australian National Survey of Mental Health and Well-Being. The 4 factors, labeled Nervous, Negative Affect, Fatigue, and Agitation, were consistent with the original scales from which the items were taken. The 2 second-order factors represent Depression and Anxiety.