Serious side effects of photodynamic therapy (PDT) are rare (A.L. Abramson, M.J. Shikowitz, M.J. Shikowitz, V.M. Mullooly, Clinical effects of photodynamic therapy on recurrent laryngeal papillomas, Arch. Otolaryngology Head Neck Surg., 118 (1992) 25–29; A.L. Abramson, M.J. Shikowitz, Clinical exacerbation of systemic lupus erythematosus after photodynamic therapy of laryngotracheal papillomatosis, Laser Surg. Med., 13 (1993) 677–679). The most frequent side effects of PDT are hypersensitive skin reactions, local edema, nausea, a metallic taste and liver-toxicity (J. Feyh, E. Kastenbauer, Treatment of laryngeal papillomatosis with photodynamic laser therapy, Laryngorhinootologie, 71 (1992) 190–192; J. Feyh, R. Gutmann, A. Leunig, Die Photodynamische Therapie im Bereich der Hals-, Nasen-, Ohrenheilkunde Laryngorhinootologie, 72(6) (1993) 273–278; M.S. Kavuru, A.C. Mekta, Treatment of recurrent respiratory papillomatosis, N. Engl. J. Med., 326 (1992) 204–205; B.L. Wenigg, D.M. Kurtzmann, Photodynamic therapy in the treatment of squamous cell carcinomas of the head and neck, Arch. Otolaryngol Head Neck Surg., 116 (1990) 1267–1270). In this case a patient (aged 57 years) suffering from a recurrent larynx papillomatosis was treated with PDT. He was sensitized with Photosan 3 (DHE) 2.5 mg kg −1 body weight, 24 h to photoradiation. As a light source, an argon dye lase, operating at a wavelength of 630 nm was used, coupled with a cylindrical light applicator. After treatment the patient was admitted to an intensive care unit for 24 h. 3 h after photoradiation, general urticarial wheals arose, as well as techycardia and a decrease in blood pressure followed by all the signs of serious anaphylaxis. 1.5 h after treatment with adrenaline and cortisone and stabilization of the cardiac and circulatory situation no more skin lesions were visible.