This study examined multiple layers of private disclosure on the microblogging site Twitter. Survey data (N = 375) were collected from current Twitter users (N = 198), nonusers (N = 116), and dropouts (N = 61). Data from current Twitter users revealed the existence of multiple strata of private disclosure boundaries on Twitter. There were significant differences at the descriptive and inferential levels among the multiple dimensions of private information, including daily lives, social identity, competence, socio-economic status, and health. Private information regarding daily lives and entertainment was disclosed easily and located at the outermost layer of the disclosure onion. In contrast, health-related private information was concealed and located within the innermost layer of the disclosure onion. ANOVAs (N = 375) also indicated that there were significant differences among current Twitter users, nonusers, and dropouts with regard to personality traits and privacy concerns about Twitter. Theoretical implications were discussed.