Maternal vitamin D deficiency is a significant public health issue. This retrospective multicentre audit was undertaken to identify the scale of maternal vitamin D deficiency in London, using infant vitamin D deficiency as a surrogate marker. During January 2006 to June 2008, 74 infants presented with symptomatic vitamin D deficiency, a prevalence of 1.6 per 1000 deliveries in London. Of these, 49% were hypocalcaemic at presentation and 27% had hypocalcaemic seizures. A telephone survey in June 2008 showed that no London National Health Service antenatal units had departmental guidelines on vitamin D. This audit is presented to raise awareness of current recommendations and the sequelae of maternal vitamin D deficiency.