The COVID-19 pandemic has induced significant impairments, including sleep disturbances. The present study aimed to explore the impact of fear in relation to stress on sleep disorders among Italian adults and older participants in the second phase of the EPICOVID19 web-based survey (January-February 2021). Sleep disturbances during the pandemic were evaluated using the Jenkins Sleep Scale, perceived stress through the 10-item Perceived Stress Scale and fear of contagion and about economic and job situation with four ad hoc items. The strength of the pathways between stress, sleep disturbances and fear was explored using structural equation modelling, hypothesising that stress was related to sleep disturbances and that fear was associated with both stress and sleep problems. Out of 41,473 participants (74.7% women; mean age 49.7 ± 13.1 years), 8.1% reported sleep disturbances and were more frequently women, employed in a work category at risk of infection or unemployed, and showed higher deprivation scores. Considering an a priori hypotheses model defining sleep and stress scores as endogenous variables and fear as an exogenous variable, we found that fear was associated with sleep problems and stress, and stress was associated with sleep problems; almost half of the total impact of fear on sleep quality was mediated by stress. The impact of stress on sleep quality was more evident in the younger age group, among individuals with a lower socioeconomic status and healthcare workers. Fear related to COVID-19 seem to be associated with sleep disturbances directly and indirectly through stress.