Younger and older adults were asked to find a single target in both feature- and conjunction- search conditions. Display size varied between 2 and 8 items, and target-distractor similarity ranged from relatively low to high levels. The accuracy data indicated that older adults had particular difficulty finding targets in high-similarity conjunction-search displays containing a large number of distractors. The reaction time (RT) analyses found larger age deficits in many of these same conditions. For both groups, predictions of conjunction search based on Treisman and Sato's additive model (Journal of Experimental Psychology: Human Perception and Performance, 1990: 16, 459-478) departed significantly from actual performance. The RT data of older observers were, in large part, predicted as a simple linear function of the young adults' data. These results are discussed with respect to age differences in selective attention, generalized slowing, and an age-related loss in search efficiency.