Trimethylaminuria (TMAU) is a rare metabolic disorder manifesting in enormous excretion of trimethylamine (TMA) with urea, sweat and breath that leads to unpleasant body odour similar to rotting fish. TMAU has a strong genetic basis: 18 mutations (associated with 17 amino acid substitutions or chain truncation) of flavin-containing monooxygenase 3 (FMO3) are now recognized as a causative factor of TMAU. Surprisingly, only few of them are related with active site structure, while the molecular basis of other mutations impact on the protein structure is unknown. Moreover, there are no FMO3 models solved experimentally. So, the aim of study was to reveal the effects of 17 known mutations on human FMO3 structure by means of structural bioinformatics techniques.