Skin cancer prevention is increasingly a focus of public health campaigns. The most important avoidable cause of skin cancer is ultraviolet radiation from the sun, but sunscreens are often used in a suboptimal manner, compromising their effectiveness. People may "compensate" for the use of sunscreen by increasing their time in the sun, which can have adverse effects on health. Epidemiologic studies of sunscreen use have suffered from important methodologic limitations. A clearer picture of the impact of sunscreens is emerging from randomized trials that have recently been published or presented. The available evidence supports the current recommendation to "Slip! Slop! Slap!" when in the sun.