Objectives. The COVID-19 pandemic has had many public health impacts, especially on vulnerable individuals including adults with neurocognitive disorders (NCD). With increasing literature, this systematic literature review aimed to address the mental health effects of COVID-19 on people with NCD in addition to examine the impact of the pandemic on treatments/resources for NCD. Methods. A literature search was conducted in the electronic databases of PubMed, PsycINFO, Web of Science and Google Scholar. Studies were included so long as they assessed the mental health or therapeutic effects of COVID-19 on NCD. Results. Among the retrieved articles, 59 met eligibility criteria. First, the pandemic and resulting self-isolation led to many detrimental effects on psychological well-being. Exacerbation and relapses of neurocognitive and behavioral symptoms were observed, as well as emergences of new psychological symptoms (i.e., depression, anxiety). Second, therapeutic and community services for individuals suffering from NCD, such as social support services and outpatient clinics, were disrupted or reduced leading to postponed appointments and evaluations, as well as reduced access to medications. These issues were somewhat palliated with the growth of telemedicine. Conclusion. This systematic review highlights the extent of the effects of the pandemic, and the topics addressed should be taken into consideration by healthcare practitioners, institutions, and policymakers to ensure that proper measures are employed to protect this population from additional harm.