To assess selective attention processes in young and old adults, behavioral and event-related potential (ERP) measures were recorded. Streams of visual stimuli were presented from left or right locations (Experiment 1) or from a central location and comprising two different spatial frequencies (Experiment 2). In both experiments, results were compared in visual-only and visual + auditory stimulus context conditions. Participants were forced to respond fast in both experiments, while maintaining high accuracy. In Experiment 1, no behavioral effects of aging were found; however, an enlargement of the N1 component in the older age group suggested that older adults initial selection process was larger than that of young adults. A late frontal effect following the P300 elicited by attended non-targets was larger in the visual + auditory condition than in the visual-only condition in the old age group. This effect was interpreted as reflecting a memory update of the relevant target location. In Experiment 2, older adults made relatively more errors in the visual + auditory condition than in visual-only condition, more so than the young adults. Older adults' ERP data were also characterized by an enlargement of the occipital selection negativity, compared to the young age group. In contrast to experiment 1, no late frontal post-P3 effect could be found, suggesting that the memory trace of the relevant stimulus feature was updated less frequently, explaining the reduction in response accuracy in the visual + auditory stimulus context conditions.