Very little is known about the influence of emotional factors on prospective memory (PM) performance. We used a mood induction (neutral or sad) to examine the effects of sad mood on time-based PM performance. Based on Ellis and Ashbrook's (1988) resource allocation model, we hypothesised an adverse effect of sad mood on PM performance. Results revealed that participants who responded to the sad mood induction procedure showed reduced PM performance that mainly resulted from a decreased timeliness of PM responses, but only in the first half of the task. Mood effects on PM could be explained in terms of reduced and less accurate monitoring. Implications for concepts of PM and the assessment of emotional after-effects are discussed.