Computer-assisted self-interview (CASI) questionnaires are being used with increased frequency to deliver surveys that previously were administered via self-administered paper-and-pencil questionnaires (SAQs). Although CASI may offer a number of advantages, an important consideration for researchers is the assessment modality's immediate and long-term costs. To facilitate researchers' choice between CASI and SAQ, this article provides theoretical cost models with specific parameters for comparing the costs for each assessment type. Utilizing these cost models, this study compared the cost effectiveness in a health behavior study in which both CASI (n = 100) and SAQ (n = 100) questionnaires were administered. Given the high initial costs, CASI was found to be less cost effective than SAQ for a single study. However, for studies with large sample sizes or when CASI software is to be used for multiple studies, CASI would be more cost effective and should be the assessment mode of choice.