Dose distribution about an 125I source in tissue has been calculated using absorbed dose constant and point isotropic source buildup factors. The effect of encapsulation material has been included. Depth-dose values have been verified by measurements with thermoluminescent dosimeters. Present data gives a value for absorbed dose constant of 1.32 rads cm2/mCi-hr. compared to the presently used value of 1.7. Depth-dose values are compared with other published data.