This study was aimed to alert the hazard of accidental adverse reactions of photochemotherapy (Psoralen-UVA or PUVA) that has been used in the treatment for some skin diseases and commercially for cosmetic tanning. Aside from the predictable side effects of PUVA such as erythema and itching, the accidental adverse reactions such as extensive burns could occasionally occur. Our observations indicated that six cases resulted from mistakes of medical personnel, and six other cases resulted from unsupervised mistakes of patients. The conditions that needed photochemotherapy were seven cases of vitiligo, three cases of psoriasis and two cases of tanning. The accidental overdose of UV radiation was about 3-10 times the empirically normal dose. Five of our patients were supposed to undergo topical PUVA, but they were irradiated at the dose of oral PUVA. One patient applied 8-methoxypsoralen (8-MOP) cream together with taking 5-methoxypsoralen (5-MOP) tablets for oral PUVA. Three other patients enjoyed sunbathing 1-3h shortly after finishing PUVA. A young couple chose 5-MOP to enhance tanning and sunbathed about 1h later. When another patient resumed PUVA in a 6-month cessation, he was exposed at a previous dose instead of a starting dose. Erythema and blisters of second degree burns developed in all our cases, 36-72h after PUVA, with 5-25% of body surface involved. Among the 12 patients, 3 were admitted and 9 were treated on an outpatient basis. All patients recovered in 1-3 weeks with no skin graft or no significant sequelae except post-inflammatory hyperpigmentation.