Whereas relations between working memory load and pupil dilation have long been established (Gardner, Beltramo, & Krinsky, 1975 ; Gardner, Philp, & Radacy, 1978 ; Granholm et al., 1996 ; Kahneman & Beatty, 1966 ), the relationship between pupil dilation and declarative memory for novel natural scenes has remained unclear. We used a 6-point confidence scale during retrieval combined with analysis of ROC slopes to verify that our observers had established declarative memories. The same method for confidence judgments has been used by others to distinguish between different models of memory according to whether an effect is observed at certain or all levels of confidence (for details, see Wixted, 2007 ). While evaluating specific memory models is beyond the scope of the present study, we intentionally designed our task virtually identical to tasks that have been used previously in a number of behavioral, functional imaging and intracranial recording studies on memory (Rutishauser et al., 2010 ; Wais et al., 2006 ; Wixted, 2007 ). Our results show that the pupil size contains information related to aspects of declarative memory formation and retrieval, thus offering a metric of potential interest for future studies of similar tasks. Our findings indicate that the stronger constriction that follows novel stimuli can be utilized to assess components of both memory formation and retrieval. We deliberately used natural scenes of varying luminance to demonstrate that this effect can be observed in relatively realistic situations. This is in contrast to some of the few previous studies that addressed familiarity effects in the pupil with words (Heaver & Hutton, 2011 ; Otero et al., 2011 ; Võ et al., 2008 ). Observers were asked to study a list of words and were later asked to indicate for another list of words whether the word was present on the previously studied list (Heaver & Hutton, 2011 ; Otero et al., 2011 ; Võ et al., 2008 ). Importantly, none of the words were novel as such. Hence, these studies did not address the formation of memory for novel items and found no significant relationship between pupil dilation and later memory performance (Võ et al., 2008 ). In contrast, we demonstrate that pupil dilation during memory formation for novel natural scenes is predictive of later memory strength, i.e., it exhibits a difference-due-to memory effect (Paller & Wagner, 2002 ) similar to what has previously been found using either invasive recordings or imaging (Johnson et al., 2009 ; Rutishauser et al., 2010 ).