[Purpose] The aim of this study was to clarify the association between the muscle tone of the ankle plantar flexors and duration of illness in patients with cerebrovascular disease (CVD). [Subjects] Seventy-four patients with CVD were the subjects of this study. [Methods] The tone of the ankle plantar flexors on the paretic side was measured in terms of the stretch reflex (SR), middle range resistance (MR), and final range resistance (FR) of the ankle plantar flexors tone scale (APTS). All APTS parameters were measured in 2 limb positions with the knee extended and flexed. The subjects were classified according to the duration of illness after onset into short- (<180 days) and long-term (>= 180 days) groups. The associations between the duration of illness and SR, MR, and FR were analyzed. [Results] In the short-term group, SR was weakly correlated with the duration of illness in both the knee extended and flexed positions. However, in the long-term group, there was no association between the SR and duration of illness in either position. [Conclusion] The results of this study suggested an increase in the stretch reflex of the gastrocnemius muscle in the patients with a duration of illness <180 days.