Objectives. We wished to determine test re-test reliability and construct validity of the star-track test of manual dexterity. Design. Test re-test reliability was examined in a controlled study. Construct validity was tested in a blinded randomized crossover study. Setting. The study was performed at a university hospital in Denmark. Participants. A total of 11 subjects for test re-test and 20 subjects for the construct validity study were included. All subjects were healthy volunteers. Intervention. The test re-test trial had two measurements with 2 days pause in between. The interventions in the construct validity study included baseline measurement, intervention 1: fatigue, intervention 2: stress, and intervention 3: fatigue and stress. There was a 2 day pause between each intervention. Main outcome measure. An integrated measure of completion time and number of errors was used. Results. All participants completed the study (test re-test n = 11; construct validity n = 20). The test re-testshowed a strong Pearson product-moment correlation (r = 0.90, n = 11, P < 0.01) with no sign of learning effect. The 20 subjects in the construct validity trial were randomized to the order of the four interventions, so that all subjects completed each intervention once. A repeated measures ANOVA determined that mean integrated measure differed between interventions (p = 0.002). Post hoc tests using Bonferroni correction revealed that compared with baseline all interventions had significantly higher integrated scores ranging from 47-59% difference in mean. Conclusion. The star track test of manual dexterity had a strong test re-test reliability, and was able to discriminate between a subject's normal manual dexterity and dexterity after exposure to fatigue and/or stress.