Objective: To determine the incidence of and factors associated with vitamin D deficiency rickets in Australian children. Design: 18-month questionnaire-based prospective observational study, using Australian Paediatric Surveillance Unit (APSU) data. Setting: Australian paediatricians and child health workers, January 2006 - July 2007. Participants: Children aged ≤ 15 years with vitamin D deficiency rickets (25-hydroxyvitamin D [25OHD] ≤ 50nmol/L, and elevated alkaline phosphatase levels [> 229 IU/L] and/or radiological rickets). Main outcome measures: Incidence of vitamin D deficiency rickets. Description of demographics, clinical presentation, identification and further analysis of overrepresented groups, and treatment regimens compared with best-practice guidelines. Results: We identified 398 children with vitamin D deficiency (55% male; median age, 6.3 years [range, 0.2-15 years]). The overall incidence in children ≤ 15 years of age in Australia was 4.9/100 000/year. All had a low 25OHD level (median, 28 nmol/L [range, 5-50nmol]) and an elevated alkaline phosphatase level (median, 407 IU/L [range, 229-5443 IU/L]), and 48 (12%) were hypocalcaemic. Ninety-five children had wrist x-rays, of whom 67 (71%) had rachitic changes. Most (98%) had dark or intermediate skin colour and 18% of girls were partially or completely veiled. Most children were born in Africa (252; 63%) and 75% of children were refugees. Duration of exclusive breastfeeding was inversely related to serum vitamin D levels in children < 3 years of age. Empirical vitamin D treatment was given to 4% of children before diagnosis. Conclusions: Vitamin D deficiency rickets is a significant problem in Australia among known high-risk groups. Public health campaigns to prevent, identify and treat vitamin D deficiency, especially in high-risk groups, are essential.