Current knowledge about burnout suffers from a healthy worker bias since only working - and thus relatively healthy - employees have been investigated. The main objective of this study is to examine - for the first time among employees who sought psychological treatment - the validity of the two most widely used burnout instruments; the Maslach Burnout Inventory (MBI) and the Burnout Measure (BM). Two groups were distinguished: a “burned out” group (n = 71) that suffers from work-related neurasthenia (according to ICD-10 criteria), and a “non-burned out” group (n = 68). Results show that: (1) the validity of the three-factor structure of the MBI and the BM is confirmed; (2) burnout can partly be differentiated from other mental syndromes (e.g., anxiety and depression); and (3) two MBI-scales (Emotional Exhaustion and Depersonalization) and one BM-scale (Exhaustion) are able to discriminate between burned out and non-burned out employees. The practical implications of these results are discussed.