Deep-seated brain tumor is difficult to treat surgically. Hyperthermia using various energy sources has been tried, but has failed to gain wide use because of equipment problems and poor temperature control. It is possible now to use Nd:YAG laser with a stable low-energy supply as an energy source for laser hyperthermia (laserthermia). Animal study and clinical study were done using SLT CL50, Computer-control Laserthermia System to treat deep-seated brain tumors. Experimental study revealed that laserthermia produced minimal edema, temperature control was satisfactory, and blood-brain barrier opened up for 6 days following laserthermia. Five patients with brain tumors were treated with laserthermia. Follow-up CT scan revealed disappearance of tumor in 4 patients and decrease in volume in 1 patient. Long-term neurological follow up revealed no deterioration. Laserthermia using Nd:YAG laser is safe and easy to use and it is beneficial to treat deep-seated brain tumors.