A compact and efficient lightpipe device to deliver light to the human oral cavity for photodynamic therapy was designed and fabricated, having dimensions 6.8 mm × 6.8 mm × 46 mm. An average irradiance of 76 mW/cm2 with an average deviation of 5% was measured on a square 25 mm2 treatment field for an input power of 100 mW. The device limits irradiation of healthy tissue and offers potential for improvement over the current treatment procedure, which requires shielding of the whole cavity to avoid damage to healthy tissue.