This paper handles the medical waste disposal facility location problem in Istanbul by using fuzzy TOPSIS (FETOPSIS) to select the adequate place between some candidate points that are obtained from the Ishii's undesirable facility location algorithm. Medical waste must be disposed without damaging environment and human health, complying with new regulations. The aim is to provide an alternative method to the medical waste disposal facility location problem in Istanbul, able to handle the fuzziness of the real world. People attempt to minimize the undesirable effects introduced by the new facility by maximizing its minimum Euclidean distance with respect to all demand points and also to minimize the total transportation costs. This study proposes a modified model of Ishii's algorithm to obtain a list of candidate points. Then a selection is made between these candidate points considering other criteria as earthquake risk, distance to natural water sources and level of air pollution.