The cholesterol-lowering effect of phytosterols has been extensively studied, and consumption of phytosterols is among the recommendations to lower LDL-cholesterol concentrations. Due to their structural similarity with cholesterol, phytosterols may undergo oxidative processes comparable to those involved in cholesterol oxidation. Consumption of phytosterols could therefore lead to increased systemic concentrations of oxidized phytosterols (oxyphytosterols) via increased dietary intake or in vivo formation from non-oxidized phytosterols. While the biological effects of oxidized cholesterol (oxycholesterol) have been well studied, the amount of biological research on oxyphytosterols is scarce. Most reports on oxyphytosterols cover their quantitative analysis. Whether oxyphytosterols may play similar biological roles as compared to oxycholesterol has not been fully elucidated. The usual perception about oxyphytosterols is that these components present a concern in terms of food quality and health. This perception originates from the parallel that is made with oxycholesterol. Yet, in line with results for oxycholesterol, recent data suggest that oxyphytosterols - depending on the type of oxidation product - may also have beneficial biological properties. Therefore, the objective of this review is to summarise the current understanding of the biological effects, next to identifying future research needs that will help to clarify the possible impact of oxyphytosterols on human health. AD - Unilever Food and Health Research Institute, 3130 AC Vlaardingen, The Netherlands.