Young adults spend a good deal of time using social network sites (SNSs), and the consequences of this activity have come under considerable scrutiny in research. There is some evidence that SNSs offer a context for young adults to engage in self-disclosure, and that such behavior may contribute to their development. In the current study, self-disclosure motivations were explored as a moderator of the relationship between SNS time use and indicators of adjustment. It was hypothesized that the relationships between SNS time use and three indicators of young adult adjustment (belonging, self-concept clarity, and flourishing) would be moderated by self-disclosure motivations. Data were collected using a cross-sectional survey of 524 young adults aged 17–25 years (Mean age = 19.75; SD = 2.16) who used at least one social network site daily (Mean hours of daily use = 3.25; SD = 1.67). The relationships between SNS time use and both belonging and flourishing were moderated by self-disclosure motivations. Specifically, when participants were low or moderately motivated to self-disclose (for relationship maintenance or self-presentation purposes) SNS time use was negatively related to belonging and flourishing. Whereas when participants were highly motivated to self-disclose there was no significant relationship between SNS time use and belonging and SNS time use and flourishing. Additionally, there was no significant moderation of the relationship between SNS time use and self-concept clarity. Based on these findings, we recommend that in order for young adults to reap potential benefits of spending time online they should endeavor to use SNSs for purposes that promote positive self and relational development.