Childhood diabetes care may be suboptimal in resource-poor countries. A cross-sectional study of youths with diabetes aged ≤19 years attending the three major paediatric centres in Vietnam was performed. Diabetes management was documented by questionnaire. Glycated haemoglobin (HbA1c) was measured with a fingerprick blood sample. Multiple linear regression analysis was used to examine factors associated with glycaemic control. In total, 105 patients participated, comprising 93 with type 1 diabetes and 12 with neonatal diabetes. The median age was 11.5 years [interquartile range (IQR) 6.4–14.5 years] and the median duration of diabetes was 2.6 years (IQR 1.5–6.1 years). Patients with type 1 diabetes performed few blood glucose tests per month (median 8, IQR 4–30). Mean HbA1c was higher in patients with type 1 diabetes compared with neonatal diabetes (9.9% vs. 7.5%; P = 0.01). In type 1 diabetes using multivariate analysis, higher HbA1c was associated with older age (β = 0.3, 95% CI 0.2–0.4; P < 0.001), lower frequency of blood glucose monitoring (β = –0.06, 95% CI –0.10 to 0.12; P = 0.01) and use of pre-mixed insulin (β = −1.7, 95% CI −3.4 to 0.0; P = 0.05). In conclusion, international glycaemic control targets for childhood diabetes (HbA1c <7.5%) are not being achieved in Vietnam, and intensive diabetes management is rare. There is an urgent need to address barriers to achieving optimal control in this population.