This study evaluates the short-term efficacy and respondents evaluations of a Web-based computer-tailored nutrition intervention, aiming to decrease saturated fat intake and increase fruit and vegetable intake. Perceived personal relevance, individualization, and interestingness of the information were tested as mediators of the effects of the tailored intervention. The objective was to study the short-term effects of a Web-based computer-tailored nutrition intervention. Respondents (N = 782) were randomly assigned to a tailored intervention group, a generic nutrition information control group, or a no-information control group. Fat, fruit, and vegetable intakes and behavioral determinants were measured at baseline and at 3 weeks postintervention. Posttest group differences were determined by multiple linear regression analyses. The computer-tailored intervention produced significant effects for the determinants of fat, fruit, and vegetable intake and for vegetable and fruit intake. The tailored information was rated as more personally relevant, individualized, interesting, and new than the generic nutrition information. Perceived personal relevance, individualization, and interestingness were identified as mediators of some of the tailoring effects. The findings of this study indicate that Web-based, computer-tailored nutrition information can have a short-term effect on the determinants of fat, fruit, and vegetable intake. The effect of the tailored information may be partly explained by the perceived personal relevance and individualization of the information.