This chapter focuses on complications of lasers. Laser and light sources have a particular therapeutic window, narrow or wide, for a particular lesion or condition. Laser-treated skin requires special care, regardless of the laser used or the lesion treated. As different lasers produce different skin responses, customized post-treatment regimens should be advocated to eliminate adverse after effects. Immediate complications of lasers are postoperative erythema and edema, blistering and crusting, irritant or allergic contact dermatitis, milia, acne form eruptions, purpura, pain and discomfort, delayed wound healing, and burns. Delayed complications are hyperpigmentation, hypopigmentation, scarring, and demarcation line. Rare complications are leukotrichia, urticaria, keloids, viral, bacterial, and fungal infections of skin, koebnerization, tingling sensation or dysesthesias or paresthesias, and superficial phlebitis.