Despite increased concern about the privacy threat posed by new technology and the Internet, in many environments there is little evidence that people’s privacy concerns lead to privacyprotecting behaviours. In the present paper, two studies are presented in which people’s privacy concerns are studied in light of their willingness to disclose personal information to web-based surveys. In Study 1, measures of privacy concern are collected, followed six weeks later by a request to complete a web-based survey containing requests for sensitive personal information, alongside measures of trust in the requestor, and perceived privacy related to the specific request (n= 759). Structural equation modelling identified two privacyrelated pathways determining self-disclosure: one based on respondents’ perceived privacy and trust (a situational pathway), the other respondents’ general privacy concerns and privacy-protecting behaviours (a dispositional pathway). In Study 2, privacy and trust were experimentally manipulated, and disclosure to a web-based survey measured. The results indicated that the impact of low privacy on self-disclosure is moderated by trust, such that high trust compensates for low privacy when examining item non-response. Implications for understanding the links between privacy attitudes, design of web-based surveys and item nonresponse to sensitive items, are discussed.