In a screen for genes expressed in the embryonic mouse facial primordia, we identified the gene sequence annotated as KIAA0101, which has previously been shown to encode a novel proliferating cell nuclear antigen (PCNA)-interacting protein named p15(PAF). We have since demonstrated that this protein also interacts in a complex with the tumour suppressor product p33ING1b, and that overexpression results in a decrease in UV-induced cell death. Although available data suggest widespread or ubiquitous expression in the adult, here we report highly restricted expression of the p15(PAF) gene in a spatio-temporal manner during mouse embryogenesis. Major sites of expression include the facial prominences, limbs, somites, brain, spinal cord and hair follicles. Based on the nature of its interacting partners, p15(PAF) is proposed to play a role in tumorigenesis. Our data also suggest a role in embryonic development, consistent with findings that a wide range of tumours result from aberrant activity of key developmental pathways.