The mineralisation disorder pseudoxanthoma elasticum (PXE) is associated with mutations in the transporter protein ABCC6. Patients with PXE suffer from calcified lesions in the skin, eyes and vasculature, and PXE is related to a more severe vascular calcification syndrome called generalised arterial calcification of infancy (GACI). Mutations in ABCC6 are linked to reduced levels of circulating vitamin K. Here, we describe a mutation in the zebrafish (Danio rerio) orthologue abcc6a, which results in extensive hypermineralisation of the axial skeleton. Administration of vitamin K to embryos was sufficient to restore normal levels of mineralisation. Vitamin K also reduced ectopic mineralisation in a zebrafish model of GACI, and warfarin exacerbated the mineralisation phenotype in both mutant lines. These data suggest that vitamin K could be a beneficial treatment for human patients with PXE or GACI. Additionally, we found that abcc6a is strongly expressed at the site of mineralisation rather than the liver, as it is in mammals, which has significant implications for our understanding of the function of ABCC6.