Data collected electronically from the World-Wide Web (WWW) in two samples (n = 429 and 1,657) were compared with traditional paper-and-pencil measure data from two university samples (n = 760 and 148) in three psychometric studies of a new measure of self-trust, the Self-Trust Questionnaire. With the exception of scale score variance, which was larger in WWW samples, psychometric properties of the scale were comparable across samples collected from the two sources. WWW samples were more similar to psychology student samples (predominantly young females) than to typical Internet users. On balance, findings indicate that the advantages of the WWW as a data source, including large heterogeneous samples, outweigh problems with data accuracy and generalizability, making the WWW an attractive source of data for researchers developing self-report personality inventories.