Excessive exposure to ultraviolet radiation (UVR) in childhood has been recognized as an extrinsic risk factor for the development of skin cancer later in life. The risk of squamous cell carcinoma is clearly related to the lifetime accumulated UVR dose, while the risk of melanoma and basal cell carcinoma is increased by intermittent UVR exposure, which is frequently responsible for sunburn. Besides UVR exposure, several intrinsic factors increase the risk of skin cancer, especially the risk of melanoma, such as skin type, the number of normal and dysplastic melanocytic naevi and family history. Responsible sun behaviour in childhood is most important to prevent skin cancer: stay in the shade, especially between 12:00 and 3:00 p.m., wear protective clothing, including a hat and sunglasses, try to build-up natural adaptation of the skin to UVR and apply a sunscreen to UVR exposed skin. There are strong indications that the possible preventive effect of sunscreens on the development of skin cancer is abolished in case of prolonged and intensive UVR exposure, because of a false feeling of safety. The most important measure to prevent the development of melanomas and basal cell carcinomas is probably the prevention of sunburn in childhood.