Narcolepsy, a chronic neurologic sleep disorder, has sparked growing interest in the potential role of vitamin B12 in its pathogenic mechanism. However, research on this association has predominantly focused on adults. Our objective was to delineate the phenotypic and genetic connections between serum vitamin B12 levels and paediatric narcolepsy.To investigate the causal relationship between vitamin B12 and paediatric narcolepsy, we conducted a retrospective analysis involving 60 narcolepsy patients and a matched control group. Univariate and multivariate logistic regression models were employed to identify independent factors influencing paediatric narcolepsy. Furthermore, a bidirectional two-sample Mendelian randomization (MR) analysis was performed to assess the causal connection between serum vitamin B12 levels and narcolepsy.Paediatric narcolepsy patients showed significantly lower serum levels of vitamin B12 and folate compared to the control group (P < 0.05). Multivariate logistic regression analysis identified serum vitamin B12 as the exclusive independent factor influencing paediatric narcolepsy (P < 0.001; OR = 0.96; 95%CI: 0.94-0.98). Additionally, IVW model results provided compelling evidence supporting a potential causal association between serum vitamin B12 levels and paediatric narcolepsy (OR: 0.958, 95% CI = 0.946-0.969, P = 0.001).This study establishes connections at both phenotypic and genetic levels, associating vitamin B12 deficiency with an increased risk of paediatric narcolepsy. These findings provide innovative perspectives for clinical strategies in the prevention and treatment of narcolepsy.© 2024 Published by Elsevier Ltd on behalf of European Paediatric Neurology Society.