Phototherapy consists in using artificial ultraviolet rays to treat chronic or chronic–recidivant dermatosis. It can be performed by adding exogenous photo-senisibilizers (PUVA and bath-PUVA) or without adding them (UBV). The latter possibility, in particular phototherapy with narrow band UBV rays, thanks to a favourable benefits/risks ratio, can be carried out with the due cautions also in paediatric age. In particular it may represent a useful therapeutic choice in psoriasis, atopical dermatitis and in vitiligo. In psoriasis the treatment can be performed in case of a diffused area, when the usage of topicals becomes problematic. In atopical dermatitis, especially in sub-acute and chronic cases, phototherapy with UVB, besides reducing itching, can have beneficial effects on the barrier function of cutis. At present it represents the first class treatment though it requires prolonged treatment cycles in generalised vitiligo. Although at the moment an increase in carcinogenic risks in the patients treated with UVB has not been demonstrated, like in all medical treatments, the usage of phototherapy requires, considering the habitually prolonged treatment and the chronicity of the treated pathologies, a careful evaluation of the risks/benefits ratio.