Morphometric analysis of 13 cell attributes in 24 stocks of 6 freshwater Paramecium morphospecies (including three sibling species of the P. aurelia complex- P. biaurelia, P. tetraurelia and P. pentaurelia) was carried out. The full morphometric data for the main freshwater Paramecium: P. caudatum, P. multimicronucleatum, P. jenningsi, P. bursaria, P. putrinum were shown for the first time. The data were compared with the authors morphometric material for the brackishwater species of the genus (25 stocks of P. calkinsi, P. nephridiatum, P. woodruffi and P. duboscqui) and P. polycaryum with the aim of revising the taxonomy of the genus (the existence of the 'putrinum', 'woodruffi' and 'aurelia' subgroups and their composition). Morphological characteristics were transformed to numerical coding and relationships among these paramecia are represented as dendrorgams and two-dimensional figures using cluster and multidimensional scaling analysis. According to this analysis, the 'aurelia' subgroup is a real cluster of species as well as the brackishwater paramecia (the 'woodruffi' subgroup without P. polycaryum). P. polycaryum is not grouped with either the 'woodruffi' or the 'aurelia' subgroups. P. bursaria and P. putrinum do not have close morphological similarity as was previously believed. They are not clustered with each other or with other paramecia. Thus, neither type of previous taxonomy (2 subgroups of Woodruff and 3 subgroups in Paramecium taxonomy of Jankowski) is supported by morphometric analysis.