Measurement of the ability of rats to traverse a narrow elevated beam has been used to quantitate motor recovery after unilateral injury to the sensorimotor cortex. Lesion extent is an important variable to consider in studies of the effects of drugs on beam-walking recovery. However, traditional histologic evaluation precludes neurochemical measurements in brain tissue. The present study was carried out to determine how well the dimensions of the lesion measured at the surface of the brain correlate with subsequent motor recovery in comparison with standard histology. The maximum medial extent of the lesion (closest approximation of the lesion to the inter-hemispheric fissure) was correlated with subsequent recovery (Spearman r = 0.61, P = 0.02) whereas the lesion surface area was not correlated with recovery (Spearman r = 0.25, P = 0.30). This data compared favorably with measures that were dependent on histologic tissue preparation. Furthermore, measurements of surface lesion parameters were highly reliable (intra- and inter-observer reliability for lesion surface maximum medial extent and lesion surface area were r2 = 0.88, 0.96, 0.97, and 0.96, P = 0.0001, respectively). Lesion surface parameters provide a valid and reliable measure of lesion size and extent for studies of beam-walking recovery after injury to the sensorimotor cortex.