OBJECTIVE: To evaluate the proportion of children and young people (CYP) tested in our emergency department (ED) who had either normal, insufficient or deficient serum levels of vitamin D to guide diagnostic strategies in the ED and neighbourhood outreach clinics in Birmingham. DESIGN: Single-centre, retrospective cohort study. SETTING: Children's ED serving a superdiverse, urban population with high levels of deprivation. PATIENTS AND INTERVENTION: All CYP aged <16 years who attended the Birmingham Children's Hospital ED and who had a serum vitamin D level sent between 1 January 2021 and 31 March 2022 were included. MAIN OUTCOME MEASURES: Primary outcome: rates of vitamin D deficiency (<25 nmol/L) and insufficiency (25-49 nmol/L) in CYP tested. SECONDARY OUTCOMES: associated laboratory biomarkers; associations between deficiency/insufficiency and patient characteristics (age, gender, ethnicity, Index of Multiple Deprivation (IMD) and seasonality). RESULTS: Of 239 CYP tested, 133 (55.6%) patients were male and mean age was 8.1 years (range 0 to 15, SD 4.8). There were 88 (36.8%) patients with vitamin D insufficiency and 62 (25.9%) who were deficient. Asian British patients had higher adjusted odds of deficiency compared with White patients (2.81 (1.11-7.85), p=0.037), but ethnicity was not associated with vitamin D insufficiency after adjustment for other patient characteristics. Increasing IMD quintile was associated with lower adjusted odds of both deficiency (OR (95% CI) per quintile: 0.59 (0.36 to 0.87), p=0.016) and insufficiency (0.58 (0.42 to 0.80), p<0.001). CONCLUSIONS: Screening is not currently advocated in the UK but we need targeted diagnostic strategies to address vitamin D deficiency in populations at greater risk.