Objective: To correct Functional Independence Measure (FIM) effectiveness for low FIM scores to obtain an index independent of FIM score on admission. Methods: A total of 1,101 stroke patients in Kaifukuki rehabilitation wards were studied. They were divided into 13 groups according to the motor FIM score on admission, in 6-point increments. The parameter "A" was derived so that motor FIM effectiveness, calculated as motor FIM gain/(Amotor FIM score on admission), was around 0.65. Results: Motor FIM effectiveness was an index independent of motor FIM score on admission when A was 42, 64, 79, 83, 87, 89,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Conclusions: Corrected FIM effectiveness, which is independent of FIM on admission, may be useful for comparisons between hospitals admitting patients with varying degrees of severity.