<p>Despite the close study of the effect of a specimen slippage under high-pressure torsion (HPT), there is still some ambiguity in this issue. In particular, the possibility of plastic flow in the specimen under slippage conditions has not been studied. In this study the effect of a specimen slippage in dies during HPT, as well as the plastic flow pattern in the specimen deformed, were experimentally studied and analyzed. Four types of materials with different deformation capabilities were used and special specimens with an insert were manufactured. HPT was performed using constrained and unconstrained die geometry, and with varying number of revolutions. The slippage effect and the plastic flow pattern were evaluated (i) by the insert displacement, (ii) by the change in the microstructure on the specimen’s cross-section, and (iii) by the change in the specimen’s microhardness. It was found that the specimen slippage effect in dies during HPT was observed when processing difficult-to-deform materials. Despite this, plastic flow develops in the specimen as a result of multiple micro-shear deformations. Moreover, with an increase in the number of revolutions, the macro-deformation of the specimen increases. The slippage effect is more pronounced in constrained die conditions compared to unconstrained die conditions.</p>