Laser beams have been in common use for the treatment of hyperpigmented skin lesions. However, therapeutic efficacy has been limited mainly because the output is circular with a Gaussian distribution of intensity, which makes it difficult to apply a uniformly distributed dose to the lesions. We have developed a technique whereby a laser beam is converted to have a square and uniform output intensity distribution. The principle of this technique is that the divergent laser beam enters a glass square pillar, propagates through the pillar repeating the total reflection and emerges with a uniform intensity distribution over the cross-section at the end of the pillar. The device applied this technique is incorporated in a hand-piece and both ruby and argon laser systems have been developed. The ruby laser has been used for the treatment of the melanistic skin lesions such as nevus cell nevus and nevus spilus. In clinical application, 36 of 67 cases have shown remarkably effective results with an improvement rate of 53.7%. The argon laser has been used for the treatment of vasogenic skin lesions such as portwine stain. In clinical application, 44 of 66 cases have shown effective results and the improvement rate is 66.7%. These results are excellent when compared with the other methods of treatment and with laser therapy previously used.