Objective: Data about vitamin B 12 (B 12 ) deficiency in the general population are scarce. The present study was performed to determine the prevalence of B 12 deficiency in the general population of the Principality of Liechtenstein, as well as to identify sub-populations potentially at high risk. Design: Retrospective study. Setting: Ambulatory setting, population of the Principality of Liechtenstein. Subjects: Seven thousand four hundred and twenty-four patients seeking medical attention whose serum samples were referred for routine work-up in an ambulatory setting were consecutively enrolled. Serum total B 12 was determined in all patients in this cohort. In addition, for a subgroup of 1328 patients, serum holotranscobalamin was also measured. Prevalence of B 12 deficiency was calculated. Further, multivariate logistical regression models were applied to identify covariates independently associated with B 12 deficiency and depletion. Results: Nearly 8 % of the general population was suffering from either B 12 depletion or deficiency. The ratio between B 12 depletion and deficiency was 2:1 for all age ranges. Pathological changes were detected predominantly in older people. Female gender was a significant predictor of B 12 depletion. In the cohort, nearly 40 % exhibited either depletion or deficiency of B 12 . Conclusions: B 12 depletion and deficiency are common in Liechtenstein, a Central European country. The measurement of biochemical markers represents a costefficient and valid assessment of the B 12 state. When a deficiency of B 12 is diagnosed at an early stage, many cases can be treated or prevented, with beneficial effects on individual outcomes and subsequent potential reductions in health-care costs.