OBJECTIVE - The objective of this study was to investigate the validity and reliability of the short-form 12-Item Well-Being Questionnaire (W-BQ12). The 12 items were used to construct the three 4-item subscales Negative Well- Being (NWB), Energy (ENE), and Positive Well-Being (PWB), and the 12-item overall scale General Well-Being (GWB). RESEARCH DESIGN AND METHODS - A total of 1,472 patients with diabetes completed the WBQI2, the Hospital Anxiety and Depression scale, and the State Trait Anxiety Inventory. Statistics covered Cronbach's α, Pearson's correlation, t tests, and logistic regression. Test- retest reliability was studied in a sample of 202 patients who twice completed the W-BQ12, which was supplemented with the Center for Epidemiological Studies Depression scale and the Short Form (5F):36 Health Survey. RESULTS - Of the tested subjects, 739 were defined as having type 1 diabetes and 701 as having type 2 diabetes. Cronbach's α proved to be high and stable across sex and type of diabetes for all W-BQ12 scales. Test-retest reliability ranged from 0.66 (PWB) to 0.83 (GWB), with a mean interval of 66 ± 14 days. Convergent validity of the W-BQ12 scales was supported by high correlations with other measures of affect. Of all scales of the first measurement, ENE proved to have the strongest association with self-reported chronic fatigue. NWB and trait anxiety both had the strongest associations with self-reported depression and current treatment by a psychologist/psychiatrist. CONCLUSIONS - The W-BQ12 appeared robe a reliable and valid measure of psychological well-being. This short instrument is easy to administer and may be considered a useful tool for both clinicians and researchers to assess the psychological well-being of patients with diabetes.