Myostatin is an extracellular cytokine mostly expressed in skeletal muscles and known to play a crucial role in the negative regulation of muscle mass. Upon the binding to activin type IIB receptor, myostatin can initiate several different signalling cascades resulting in the upregulation of the atrogenes and downregulation of the important for myogenesis genes. Muscle size is regulated via a complex interplay of myostatin signalling with the insulin-like growth factor 1/phosphatidylinositol 3-kinase/Akt pathway responsible for increase in protein synthesis in muscle. Therefore, the regulation of muscle weight is a process in which myostatin plays a central role but the mechanism of its action and signalling cascades are not fully understood. Myostatin upregulation was observed in the pathogenesis of muscle wasting during cachexia associated with different diseases (i.e. cancer, heart failure, HIV). Characterisation of myostatin signalling is therefore a perspective direction in the treatment development for cachexia. The current review covers the present knowledge about myostatin signalling pathways leading to muscle wasting and the state of therapy approaches via the regulation of myostatin and/or its downstream targets in cachexia.