ObjectivesThis study examined the association between intensive rehabilitation for subacute stroke patients and medical costs and readmission ratio during the year after discharge. DesignThis was a natural experiment study. Setting and ParticipantsWe identified individuals with a diagnosis of cerebrovascular disorder (ICD-10: I60-I69 cerebrovascular disease) in an insurance claims database in Japan from January 2005 to December 2017. From the database, 980 patients who were admitted to a convalescent rehabilitation unit with stroke were identified. After excluding 575 patients, 405 were eligible for the study. MethodsIn Japan, from April 2011, a new policy was established that allows special costs to be added as rehabilitation time increases. This policy provides an additional medical fee for inpatients in a convalescent rehabilitation unit who receive more than 120 minutes of rehabilitation therapy. We defined high-intensity rehabilitation as transfer from hospitalization to a convalescent rehabilitation unit after April 2011. Outcomes were total direct medical costs and readmission ratio during the year after discharge from the convalescent rehabilitation unit. ResultsDaily rehabilitation time, total rehabilitation time, and total medical costs of the high-intensity rehabilitation group were significantly higher than those of the low-intensity rehabilitation group (P < .001, P < .001, P = .011, respectively). However, there was no significant difference in the medical costs during the year after discharge (P = .653) or in the readmission ratio (hazard ratio: 1.09, 95% confidence interval: 0.55-2.18, P = .804). Conclusions and ImplicationsIntensive rehabilitation did not reduce medical costs or the readmission ratio during the first year after discharge. Future studies should consider the necessary rehabilitation intensity given the severity of the patient's condition, using large sample sizes.