Impaired self-awareness of deficits has been referred to in literature as anosognosia, unawareness, denial of deficits and impaired insight. In this article we briefly present the terminology used in studies of impaired self-awareness in neurological disorders and we review the literature on self-awareness of deficits in Huntington's disease (HD) and Parkinson's diseases (PD) in terms of daily function, motor impairment, cognitive function and social-emotional function in both HD and PD. HD patients may exhibit impaired self-awareness of deficits in all domains, regardless of the cognitive status, while impaired self-awareness of deficits in PD is linked to dementia. Both HD and PD patients may be unaware of involuntary movements. Only one of the reviewed studies aimed at comparing the self-awareness of deficits in PD and HD, which indicates that further research addressing this topic is needed. Next, theoretical explanations of unawareness of involuntary movements based on psychodynamic, cognitive and neurophysiological approaches are presented. Finally, the methodological shortcomings of the reviewed articles are discussed, alongside with the recommendations for future studies.