Background: Loneliness is becoming progressively more frequent despite increasing communication facilities. The COVID lockdown and social interaction restrictions enhanced loneliness complaints in more vulnerable groups while increasing its global prevalence.

Objective: To evaluate the prevalence, characteristics, and predictors of loneliness complaints during COVID19.

Methods: The sample includes 5230 participants, 67.7% female, mean age 48.6 years and SD 14.30. To assure complexity/ diversity, an extensive internet survey with 177 questions was applied during the first COVID-19 pandemic wave in Portugal, including data from the Continent and Islands (Madeira and Azores).

Results: The prevalence was higher in females, emerging adults, those living alone, living in a flat, and in a big city. The following variables were higher in LG (Loneliness Group): Stress, depression, anxiety, irritability, worries, Calamity Experience Check List (CECL), economic problems, Sleep latency and Awakenings, Screen time in TV, Mobile, Social networks, negative attitudes and negative behaviors, dependences from TV, Social networks and Games, morbidities, worsening of previous morbidities, and nightmares. The predictors were civil status, living alone, and having negative attitudes during the pandemic. 

Conclusion: The study allows us to conclude that loneliness during the COVID-19 pandemic was associated with health, psychological, behavioral, lifestyle, and housing-related factors; it could be predicted by the Calamity Experience Check List (CECL); Frequency of sexual activity; Negative attitudes; Positive attitudes; Negative Behaviors; Civil status; Living alone; Sleep latency weekdays; Sleep latency weekends. There were gender similarities and differences in loneliness predictors.