Anticholinergic drugs are frequently used in psychiatry for the prophylaxis and treatment of extrapiramidal symptoms caused by neuroleptics. Abuse of anticholinergic agents has been reported in patients with psychotic disorders, on treatment with neuroleptics, and polysubstance use disorders. We are reporting the case of a patient who presented with hypoactive delirium as a consequence of biperiden dependence. The clinician must pay special attention to detect anticholinergic misuse in patients presenting with delirium of unknown cause.