Housing modification is an effective means for elderly and disabled people to continue living in their home. However, it is difficult for renters to modify rental housing in Japan. Sometimes housing modification by the renter is referred to a judicial court. The purpose of this study is to collect and analyze information about housing modifications that have been done in rented houses. Forty-eight such cases were investigated. The following results were obtained. In 42 cases, contract cancellation was contested for the reason of housing modification by the renter. In 6 cases, the cost related to modification was contested. The contracts of 20 of the 42 cases where housing modifications had been carried out were rescinded, while those of the other 22 were not. Renters were not required to give up their lease if the following conditions were met: 1) the modification work did not affect the structure of the building; 2) the modifications met social demands; 3) the modifications restored the house to its original condition; 4) the value of the housing unit had increased and it was possible to restore the unit to its original condition. It was concluded that modifications could be carried out without the authorization of the lessor if these four conditions were met.