Population norms for interpretation of fatigue measurements have been lacking, and the sociodemographic associations of fatigue are poorly documented. A random sample of 3500 Norwegians, aged 19-80 years, was therefore investigated. A mailed questionnaire included the fatigue questionnaire (11 items) in which the sum score of the responses (each scored 0, 1, 2, 3) is designated as total fatigue (TF). Sixty-seven percent of those receiving the questionnaire responded. Women (TF mean=12.6) were more fatigued than men (TF mean=11.9), and 11.4% reported substantial fatigue lasting 6 months or longer. TF and age were weakly correlated (men: r=0.17; women: r=0.09). No firm associations between fatigue and social variables were found. Disabled and subjects reporting health problems were more fatigued than subjects at work or in good health. Fatigue is highly prevalent in somatic and psychiatric disorders, but is often neglected. This national representative sample provides age- and gender-specific norms that will allow for comparisons and interpretations of fatigue scores in future studies.