The Internet has become increasingly popular as a way to administer self-report questionnaires, especially in the field of Internet delivered psychological treatments. Collecting questionnaire data over the Internet has advantages, such as ease of administration, and automated scoring. However, psychometric properties cannot be assumed to be identical to the paper-and-pencil versions. The aim of this study was to test the equivalence of paper-and-pencil and Internet administered versions of self-report questionnaires used in social phobia research. We analyzed data from two trials in which samples were recruited in a similar manner. One sample (N = 64) completed the paper-and-pencil version of questionnaires and the second sample (N = 57) completed the same measures online. We included the Liebowitz Social Anxiety Scale-self-assessment (LSAS-SR), the Social Interaction and Anxiety Scale (SIAS), and the Social Phobia Scale (SPS) as measures of social anxiety. Also included were the Montgomery Åsberg Depression Rating Scale-self-assessment (MADRS-S), the Beck Anxiety Inventory (BAI), and the Quality of Life Inventory (QOLI). Results showed equivalent psychometric properties across administration formats. Cronbach’s α ranged between 0.77 and 0.94. There was an indication of a somewhat higher construct validity when participants filled out questionnaires using paper-and-pencil. We conclude that the LSAS-SR, SIAS, and SPS can be administered via the Internet with maintained psychometric properties.