Objective To investigate (a) the applicability of the proportional recovery rule of spontaneous neurobiological recovery to motor function of the paretic lower extremity (LE); and (b) the presence of fitters and non-fitters of this prognostic rule poststroke. When present, the clinical threshold for fitting nor non-fitting would be determined, as well as within-subject generalizability to the paretic upper extremity (UE). Methods Prospective cohort study in which the Fugl-Meyer Assessment (FMA)-LE and FMA-UE were measured <72 hours and 6 months poststroke. Predicted maximum potential recovery was defined as [FMA-LEmax−FMA-LEinitial = 34 –FMA-LEinitial]. Hierarchical clustering in 202 first-ever ischemic stroke patients distinguished between fitting and not fitting the rule. Descriptive statistics determined whether fitters and non-fitters for LE were the same persons as for UE. Results 175 (87%) patients fitted the FMA-LE recovery rule. The observed average improvement of the fitters was ~64% of the predicted maximum potential recovery. In the non-fitter group, the maximum initial FMA-LE score was 13 points. Fifty-one out of 78 patients (~65%) who scored below the identified 14-point threshold at baseline fitted the FMA-LE rule. Non-fitters were more severely affected than fitters. All non-fitters of the FMA-LE rule did also not fit the proportional recovery rule for FMA-UE. Conclusions Proportional recovery seems to be consistent within subjects across LE and UE motor impairment at the hemiplegic side in first-ever ischemic hemispheric stroke subjects. Future studies should investigate prospectively distinguishing between fitters and not-fitters within the subgroup of patients who have initial low FMA-LE scores. Subsequently, patients could be stratified based on fitting or not fitting the recovery rule as this would impact rehabilitation management and trial design.