Although there exists a consensus that depression is characterized by preferential processing of negative information, empirical findings to support the association between depression and rumination on the one hand and selective attention for negative stimuli on the other hand have been elusive. We argue that one of the reasons for the inconsistent findings may be the use of aggregate measures of response times and accuracies to measure attentional bias. Diffusion model analysis allows to partial out the information processing component from other components that comprise the decision-making process. In this study, we applied a diffusion model to an emotional flanker task. Results revealed that when focusing on a negative target, both rumination and depression were associated with facilitated processing due to negative distracters, whereas only rumination was associated with less interference by positive distracters. After controlling for depression scores, rumination still predicted attentional bias for negative information, but depression scores were no longer predictive after controlling for rumination. Consistent with elusive findings in the literature, we did not find this pattern of results when using accuracy scores or mean response times. Our results suggest that rumination accounts for the attentional bias for negative information found in depression. © 2013 American Psychological Association.