Monoclonal gammopathy of undetermined significance (MGUS)-associated involvement of the peripheral nervous system is widely reported in the literature. At the same time, involvement of central nervous system (CNS) occurs far less frequently. Analysing the reported cases, almost all the authors pose the question whether there is a relationship between CNS involvement and MGUS, and at what stage it is necessary to begin therapy of haematological disorders. The limited number of reported cases precludes us from getting a definite answer to these questions, thus making further accumulation of clinical data highly relevant. In this article, we present two cases of CNS involvement in patients with MGUS, which, in our opinion, may suggest the existence of a causal relationship between MGUS and CNS involvement. Currently, the above hypothesis cannot be taken as proved due to the lack of a sufficient number of clinical observations and scientific studies. Therefore, the issue of MGUS-associated CNS involvement requires further research.