Inborn errors of metabolism (IEM) comprise a heterogeneous group of more than 1000 diseases with extreme clinical variability and severity of manifestation. These disorders often present themselves mainly in childhood. However, a number of less severe and lateronset forms often with a varied psychiatric manifestation (PM) has been described lately. Since the diseases are rare, clinical experience with particular disorder is usually diminutive. The aim of this work is to shed light upon the issue of PM in patients with IEM, to outline the principles of the pathophysiology of IEM and to raise awareness of this group of disorders upon examples of selected diseases case reports. Cautionary signs of PM of IEM can be familial occurence and early onset of the disease, conspicious fluctuation of clinical signs, cognitive deterioration, visual hallucinations, presence of catatonia, resistance to common treatment, higher frequency of adverse events of the therapy or even worsening of PM after its commencement. Typical examples of such disorders are urea cycle defects, disorders of sulfur amino acids metabolism, acute porphyrias, Niemann-Pick disease type C, Tay-Sachs disease, adult form of metachromatic leukodystrophy, X-linked adrenoleukodystrophy, Wilson disease and mitochondrial diseases. The diagnostics is intricate and ought to be conducted in cooperation with a specialised centre. Its importance is emphasized by the availability of effective therapy for a number of these disorders. [ABSTRACT FROM AUTHOR]