The ability of NICMOS to perform high accuracy polarimetry is currently hampered by an uncalibrated residual instrumental polarization at a level of 1.2 - 1.5 \% . To better quantify and characterize this residual we obtained observations of three polarimetric standard stars at three separate space-craft roll angles . Combined with archival data , these observations were used to characterize the residual instrumental polarization to enable NICMOS to reach its full polarimetric potential . Using these data , we calculate values of the parallel transmission coefficients that reproduce the ground-based results for the polarimetric standards . The uncertainties associated with the parallel transmission coefficients , a result of the photometric repeatability of the observations , dominate the accuracy of p and \theta . However , the new coefficients now enable imaging polarimetry of targets with p \approx 1.0 \% at an accuracy of \pm 0.6 \% and \pm 15 \hbox { $ { } ^ { \circ } $ } .