This study investigated how the ability to extend the fingers and thumb recovers early after stroke and how the ability to extend all of the digits affects grasping performance. We studied 24 hemiparetic patients at 3 and 13 weeks post stroke. At each visit, we tested subjects' ability to actively extend all 5 digits of their contralesional, affected hand against gravity and to perform a grasp movement with the same hand. Three-dimensional motion analysis captured: 1) maximal voluntary extension excursion of each digit, and 2) grasp performance variables of movement time, peak aperture, peak aperture rate, and aperture path ratio. We found that finger and thumb extension improved from 3 to 13 weeks, with average improvements ranging from 12 - 19 degrees across the five digits. Grasp performance improved on 2 of the 4 variables measured. Peak apertures and peak aperture rates improved from 3 to 13 weeks, but self-selected movement time and aperture path ratio did not. Stepwise multiple regression models showed that the majority of variance in grasp performance at 13 weeks could be predicted by the ability to extend the index or middle finger at 3 weeks, plus the change in the ability to extend the index finger from 3 to 13 weeks. R2 values ranged from 0.55 - 0.89. Our data indicate that the amount of recovery in finger and thumb extension and grasping is small from 3 to 13 weeks post stroke. In people with relatively pure motor hemiparesis, one important factor underlying deficits in hand shaping during grasping is the inability to extend the fingers and thumb. Without sufficient volitional control of finger and thumb extension, successful grasping of objects will not occur.