A new clinical test of dynamic standing balance, called the Step Test, has been developed to evaluate dynamic single limb stance. This aspect of balance is not adequately assessed in other reported balance tests and may be important in identifying balance problems during common potentially destabilizing activities, such as locomotion, for stroke patients. The Step Test involves stepping one foot on, then off, a block as quickly as possible in a set time period. Forty-one healthy elderly subjects (mean age 72.5, 44% males), and 41 stroke patients undergoing in-patient rehabilitation (mean age 72.5, 54% males) were assessed, on average 54 days post-stroke. Retest reliability was high in a subgroup of 14 healthy subjects (Intraclass Correlation Coefficents, ICC>0.90) and 21 stroke patients (ICC>0.88). Performace on the Step Test by the stroke group was significantly lower than that of the healthy elderly group (p<0.001), with only 4.8% scoring within one standard deviation of the healthy elderly mean score. Performance on the Step Test correlated significantly with Functional Reach and gait velocity and stride length (p<0.001). Based on the results of this study, it is recommended that the Step Test form part of a balance test battery for stroke patients.