The present research investigated whether the attribution process through which people explain self-disclosures differs in text-based computer-mediated interactions versus face to face, and whether differences in causal attributions account for the increased intimacy frequently observed in mediated communication. In the experiment participants were randomly assigned to a face-to-face or computer-mediated interaction with a confederate who made either high- or low-intimacy self-disclosures. Results indicated that computer-mediated interactions intensified the association between disclosure and intimacy relative to face-to-face interactions, and this intensification effect was fully mediated by increased interpersonal (relationship) attributions observed in the computer-mediated condition. The article presents an attributional extension of the hyperpersonal model (Walther, 1996) by demonstrating the role of causal attributions in interpersonal intensification processes in text-based computer-mediated interactions. (Contains 1 note, 2 tables, and 2 figures.)