Mirror movement (MM), or visible involuntary movements of a relaxed hand during voluntary fine finger movements of an activated opposite hand, can be observed in the hand that is on the unaffected side of patients with stroke. In the present study, we longitudinally examined the relationship between voluntary movement of the affected hand and MM in the unaffected hand in a single case. We report a 73-year-old woman with a right pontine infarct and left moderate hemiparesis. MM was observed as an extension movement of the unaffected right index finger during extension movement of the affected left index finger. The affected right index movement was found to increase, while MM of the unaffected left index finger was observed to decrease with time. These results indicate that the assessment of MM might be useful for studying the process of motor recovery in patients with stroke.