Nearly 50 years ago the first reports appeared that cast suspicion on lipids, or peroxidative products thereof, as being involved in the expression of actinically induced cancer. Whereas numerous studies have implicated lipids as potentiators of specific chemical-induced carcinogenesis, only recently has the involvement of these dietary constituents in photocarcinogenesis been substantiated. It has now been demonstrated that both level of dietary lipid intake and degree of lipid saturation have pronounced effects on photoinduced skin cancer, with increasing levels of unsaturated fat intake enhancing cancer expression. The level of intake of these lipids is also manifested in the level of epidermal lipid peroxidation. Conversely, dietary antioxidants inhibit both lipid peroxidation and photocarcinogenesis, the degree of inhibition of the latter being roughly equivalent to the degree of cancer enhancement evoked by the respective level of dietary lipid. The apparent similarities of lipid effects on both chemical and photoinduced carcinogenesis suggest a common underlying role for these dietary constituents in the carcinogenic process. This role may involve free radical-mediated lipid peroxidative reactions. Regardless of the mechanism, it is obvious that both dietary lipid and antioxidants can modify the photocarcinogenic response of skin.