Although most events are sponsored by more than one firm, the impact of roster size, or number of sponsors, on sponsorship effectiveness has received scant research attention. Two studies investigate the hypothesized moderating effect of roster size on consumer evaluations of events. Study 1 shows that compared with one-sponsor conditions, an increased number of sponsors dilutes the benefits obtained from consumers inferring a goodwill sponsorship motive and enhances attitudes under sales motives conditions. Study 2 shows that compared with one-sponsor conditions, an additional sponsor reduces the negative effect of being associated with stigmatized event beneficiaries. The results have implications for sponsorship theory, as well as practical implications for event promoters and the firms they seek to attract as sponsors. © 2006 American Academy of Advertising. All rights reserved.