Prospective memory slips (forgetting to do something) are as part of everyday memory failure as retrospective complaints (forgetting a past event). The extent to which genes influence prospective and retrospective memory is so far unclear. This study aims to quantify the relative genetic and environmental influences on such memory slips and seeks to identify QTL's with the first genome-wide scan for such traits. A classic twin design was implemented: comprising 896 monozygotic (MZ) and 1008 dizygotic (DZ) female twin pairs aged between 19 and 85 (mean age, 51) participated. The prospective and retrospective memory questionnaire (PRMQ) consists of 16 items, eight asking about prospective memory failures and eight concerning retrospective failures. Heritability for prospective memory and retrospective memory were found to be 44% and 41%, respectively. A genome- wide scan of 489 female DZ twin pairs suggested a QTL on chromosome 12q22 for prospective memory (LOD 2.76, empirical p-value 0.0006). Within this QTL lies an obvious candidate-the SCAD gene. These results suggest that large-scale gene discovery studies are possible with self-report memory questionnaires.