Background In the spring of 2020, Belgian authorities enforced a full lockdown period to contain the spread of the SARS-CoV-2 virus. This lockdown drastically disrupted the daily life of autistic individuals’ and that of their families. In the midst of these extraordinary circumstances, we assessed the impact of social restrictions on autistic individuals’ behavior and their parents’ or caregivers’ quality of life; we also sought to identify individual characteristics that may influence such changes. Methods We designed an online survey targeting caregivers living with an autistic child or adult. The questionnaire included 125 five-point Likert questions which targeted changes in families’ quality of life and in autistic individuals’ behavior, as well as factors likely to influence the extent and direction of these changes. Results We collected data from 209 French-speaking Belgian respondents. Respondents reported that the lockdown brought about a higher frequency of nonfunctional socio-communicative behaviors, as well as a decrease in families’ quality of life. Parents who had less access to respite care experienced a steeper decrease in their quality of life. Autistic individuals with comorbidities, and whose parents had less access to respite care and implemented fewer rules at home during lockdown were more likely to display nonfunctional socio-communicative behaviors. Conclusion COVID-19 lockdown restrictions had a negative impact on both autistic individuals and their parents.