Massive amounts of information about others are disclosed across the world on social network sites every day. Disclosure of information about others may precipitate unanticipated consequences such as violating the privacy of another individual. Previous social network site (SNS) research has examined self-disclosure, this research examines the disclosure of information about others (DIO), building upon the theory of planned behavior and through the lens of Rest's ethical derision making model. A person's concern about others' privacy (COP) when he/she wants to share information about them is different from concern for himself/herself. The authors tested the posited model, using data collected with a survey instrument. Findings show that the COP, and attitude toward using SNSs influence the intention to disclose information about others. Also, COP is explained by social identity, agreeableness, extraversion, opinion leadership, sensitive information disclosure control, and prior privacy invasions. Social norms do not influence intentions to disclose information about others. Results indicate males have higher concern about others' privacy than females. This research contributes to the understanding of ethical choices of information disclosure within SNSs. Findings can help SNS developers improve privacy practices, protect sensitive third-party information, and improve user satisfaction. Published by Elsevier Ltd.