There are many types of adaptive design and one of them is sample size re-estimation. It may provide the flexibility in clinical trial studies and may have the potential in increasing the chance of obtaining positive results from a trial (power). The application of sample size re-estimation in confirmative trial design is reviewed and issues are raised and discussed from a statistical reviewer’s stand point. A hypothetical example is presented for discussion for issues in this field, especially the one on sample size re-estimation approach using simulation study.