Laser{induced thermo therapy (LITT) is an alternative, gentle therapy of cancer. In this work a new computa- tional model (3D space and time) of LITT is presented. Using an arbitrary small number (<20) of optical ¯bers, multiple low energy laser light sources are applied internal to an arbitrary shaped tumor in the human liver. The power and position of each source can be chosen arbitrary. Each source is a spherical point source emitting light isotropically. The model consists of two, semi{coupled partial di®erential equations (PDEs) describing the light distribution and the heat absorption in the target tissue. Since water is a dominant tissue component in both the healthy liver and the malignant tumor the wavelength of the laser is chosen in the NIR area (1,064 nm). This is expected to form an absorption contrast in favor of the tumor leading to high temperature and damage of the tumor cells. The new, fast computational model presented here opens for the possibility of evaluating the outcome of LITT by inspection of temperature ¯elds, and comparing these to measured histological damage due to heating. This combination is promising when evaluating the result of LITT prior to the actual treatment.