Riboflavin (RF), commonly known as vitamin B2, is an essential component of living organisms, and it is also an efficient photosensitizer, widely used by chemists for modifying organic molecules that do not absorb visible light. Since the pioneer work by Wang (Photochem. Photobiol., 1975, 21, 373–375), who demonstrated that daylight fluorescence lamps have a lethal effect on human cells in culture media, many works have appeared concerning the toxic effect of RF photosensitization in biological systems; the effects on DNA, lipids and amino acids and proteins have been discussed. The mechanisms involved in light-induced cell toxicity of RF have not yet been elucidated. The possibility of inducing apoptosis in cells and tissues showing inhibition of this cell death mechanism (high proliferating tissues) has increased the interest in the research in this area.