Objective: To validate a short English-language version of the Temperament Evaluation of Memphis, Pisa, Paris and San Diego-autoquestionnaire version (TEMPS-A), a self-report questionnaire designed to measure temperamental variations in psychiatric patients and healthy volunteers. Its constituent subscales and items were formulated on the basis of the diagnostic criteria for affective temperaments (cyclothymic, dysthymic, irritable, hyperthymic, and anxious), originally developed by the first author and his former collaborators. Further item wording and selection were achieved at a later stage through an iterative process that incorporated feedback from clinicians, researchers, and research volunteers. Method: A total of 510 volunteers (284 patients with mood disorders, 131 relatives of bipolar probands, and 95 normal controls) were recruited by advertisement in the newspapers, announcements on radio and television, flyers and newsletters, and word of mouth. All participants were interviewed using the Structured Clinical Interview for DSM-III-R, and completed the 110-item TEMPS-A and the Temperament and Character Inventory (TCI-125). The factorial structure, the α coefficients, and the item–total correlations coefficients of the TEMPS-A and the correlation coefficients between the dimensions of the TCI and the TEMPS-A subscales were then determined. Results: A principal components analysis with a Varimax rotation found that 39 out of the 110 original items of the TEMPS-A loaded on five factors that were interpreted as representing the cyclothymic, depressive, irritable, hyperthymic, and anxious factors. Coefficients α for internal consistency were 0.91 (cyclothymic), 0.81 (depressive), 0.77 (irritable), 0.76 (hyperthymic), and 0.67 (anxious) subscales. We found statistically significant positive correlations between all—but the hyperthymic—subscales and harm avoidance. Positive correlations with the hyperthymic and cyclothymic, and novelty seeking and negative correlations with the remaining subscales were also recorded. Other major findings included positive correlations between the hyperthymic and reward dependence, persistence and self-directedness; positive correlation between the self-transcendence and the cyclothymic, hyperthymic and the anxious; and negative correlations between the depressive, cyclothymic, irritable, anxious and cooperativeness. Limitation: As the full-scale anxious temperament was added after the four scales of the TEMPS-A were developed, it has only been evaluated in 345 subjects. Conclusions: These data indicate that the TEMPS-A in its shortened version is a psychometrically valid scale with good internal consistency. The proposed five subscale structure is upheld. Concurrent validity against the TCI is shown. Most importantly, for each of the temperaments, we were able to show positive attributes which are meaningful in an evolutionary context, along with traits which make a person vulnerable to mood shifts. This hypothesized dual nature of temperament, which is upheld by our data, is a desirable characteristic for a putative behavioral endophenotype in an oligogenic model of inheritance for bipolar disorder.