This study investigated the effect of a motivational manipulation on naturalistic time-based prospective memory (PM) task performance. The association between depression and PM task performance was also investigated. First-year psychology students were required to send mobile phone text messages (SMSs) at a specific time 3 days and 6 days after an initial meeting. During the delay period participants recorded details of the retrieval whenever they remembered the SMS task. Participants given the incentive of extra course credit (motivation condition) outperformed their counterparts on the PM tasks, and showed a greater increase in the reported frequency of self-initiated retrievals on target days. Depression was negatively correlated with PM task performance. The findings suggest that motivational instructions impact the controlled processes underlying PM.