COVID-related lockdown led to a radical modification of daily activities and routines which are known to affect sleep. Compared to the general population, participants with autism may be particularly vulnerable to the repercussions of lockdown on sleep, given their intrinsic inflexible adherence to routines and the high overall prevalence of sleep disturbances in this population. The study is a French nation-wide online survey assessing sleep-wake rhythms and behaviors known to affect sleep (daily screen time, daylight exposure, and physical activity), before and during COVID-related lockdown. Respondents were 207 adults with autism (56% female) and 1652 adults of the general population (77% female), with a mean age 35.3 years (SD 11.3). Before lockdown, the adults with autism displayed on average later bedtime and waking hours, lower sleep quality, more evening screen time, less exposure to daylight, and less exercise (all p < 0.01). Lockdown affected all studied measures of sleep and related exposures in a similar way in both groups: poorer self-rated sleep quality as well as a less regular and delayed sleep-wake rhythm, longer screen time in the evening and less exposure to daylight (all p < 0.001). Adults with autism displayed significantly higher levels of sleep and circadian rhythm disturbances and less favorable daily routines known to regulate sleep. While the effect of confinement on sleep and sleep related behaviors was similar in both groups, the results highlight that the preexisting shift in circadian rhythms and lifestyles in adults with ASD further deteriorated during lockdown. Lay abstract: COVID-related lockdown led to a radical modification of daily activities and routines known to affect sleep. In a sample of 1800 adults, we observed that, before lockdown, participants with autism displayed significantly higher levels of sleep disturbances and less favorable daily routines known to regulate sleep, compared to the general population. While the deleterious effect of lockdown on sleep was similar in both groups, pre-existing difficulties in adults with autism reached worrying levels during lockdown. K E Y W O R D S autism spectrum disorder, circadian rhythm, insomnia, sleep, sleep hygiene Eve Reynaud and Julien Pottelette are co-first authors. Romain Coutelle and Carmen M. Schröder are co-last authors.