A lack of deceased kidney donors in Japan has led to dependence on living donors in as many as 80% of cases. At the same time, indications for living-donor kidney donation have been expanding in terms of donor medical status as well as HLA matching and ABO compatibility, thus emphasizing the donor shortage. To facilitate final medical decision-making for living kidney donation, we attempted kidney biopsy in six donor candidates who had problems such as mild diabetes and slight proteinuria. The biopsy specimens showed various degrees of tissue injury ranging from partial glomerular sclerosis to arteriole hyalinization. On the basis of the biopsy findings, kidney donation was subsequently performed in three of the six cases with full informed consent, and not done in the remaining three cases. Longer-term studies will be needed to clarify the outcome in both the donors and recipients in these cases.