The paper provides an overview of age-differences in patients' preferences for participation in cancer treatment decision-making and factors that relate to these age-differences. On average, older cancer patients prefer to receive less information about their illness and treatment and assume a less active role in making treatment decisions. They are also less likely to collect and analyze all relevant information in order to make an optimal decision. Observed age-differences are, in part, explained by age-associated cognitive decline. Age-differences are, on average, small to moderate, and most older patients prefer to be well-informed. Nonetheless, only a minority of them wishes to play an active role in decision-making. Given their lower preference for active participation in decision-making, older adults may show less positive psychological effects of active participation, but this question warrants research. Implications for working with older cancer patients are discussed.