The purpose was to investigate the impact of the COVID-19 pandemic on biopsychosocial health, daily activities, and quality of life among children and adults with neuromuscular diseases, and to assess the prevalence of COVID-19 infection and the impact of this in patients with neuromuscular diseases. The study was a national questionnaire survey. Responses were obtained from 811 adults (29%) and 67 parents of children (27%) with neuromuscular diseases. Many patients reported decreased health or physical functioning, and changes in access to physiotherapy or healthcare due to the pandemic. Participants generally perceived themselves or their child to be at high risk of severe illness from COVID-19, but only 15 patients had suffered from COVID-19 and experienced mild flu-like symptoms. 25.3% of adults and 46.6% of parents experienced anxiety. 20.4% of adults and 27.6% of parents experienced symptoms of depression. In general, the pandemic contributed to anxiety, a depressed mood as well as to fewer leisure activities, less social contact, isolation from work/school and a reduced quality of life, in particular for patients who perceived themselves to be at high risk of severe illness. The results demonstrate that the pandemic has had a negative impact on biopsychosocial health and quality of life of patients with neuromuscular diseases.