11-hydroxysteroid dehydrogenase type 1 (11-HSD1) converts inert 11keto-glucocorticoids to active 11-hydroxy forms, thereby amplifying intracellular glucocorticoid action. Up-regulation of 11-HSD1 in adipose tissue and liver is of pathogenic importance in metabolic syndrome. However, the mechanisms controlling 11-HSD1 transcription are poorly understood. Glucocorticoids themselves potently increase 11-HSD1 expression in many cells, providing a potential feed-forward system to pathology. We have investigated the molecular mechanisms by which glucocorticoids regulate transcription of 11-HSD1, exploiting an A549 cell model system in which endogenous 11-HSD1 is expressed and is induced by dexamethasone. We show that glucocorticoid induction of 11-HSD1 is indirect and requires new protein synthesis. A glucocorticoid-responsive region maps to between -196 and -88 with respect to the transcription start site. This region contains 2 binding sites for C/EBP that together are essential for the glucocorticoid response and which bind predominantly C/EBP, with C/EBP present in a minority of the complexes. Both C/EBP and C/EBP are rapidly induced by glucocorticoids in A549 cells, but siRNA-mediated knockdown shows that only C/EBP reduction attenuates the glucocorticoid induction of 11-HSD1. Chromatin immunoprecipitation studies demonstrated increased binding of C/EBP to the 11-HSD1 promoter in A549 cells following glucocorticoid treatment. A similar mechanism may apply in adipose tissue in vivo where increased C/EBP mRNA levels following glucocorticoid treatment were associated with increased 11-HSD1 expression. C/EBP is a key mediator of metabolic and inflammatory signaling. Positive regulation of 11-HSD1 by C/EBP may link amplification of glucocorticoid action with metabolic and inflammatory pathways and may represent an endogenous innate host-defence mechanism.