Cryosurgery has been used to treat various nonresectable tumors, and although it is known to have great safety, and minimal morbidity, and mortality, we experienced unexpected hypothermia during thoracoscopic cryosurgery for metastatic lung cancer. Even though arrythmia and coagulopathy were absent in our case, it is possible to experience such complications in cases of long duration cryosurgery. We report out experience and include a brief discussion of the issues involved.