The worldwide outbreak of CoronaVirus Disease appeared in 2019 (COVID-19) has forced millions of people into social isolation. Past research has documented negative psychological effects of self-isolation during health crises, in terms of stress, anger or depressive symptoms, but overall ignored psychotic symptoms and cognitive problems. The present study (n = 211) examined the relationship between the conditions of self-isolation – that is, duration, living space, frequency of social interactions – and psychotic symptoms and cognitive problems during the COVID-19 outbreak. The frequency of both psychotic symptoms and cognitive problems was asso- ciated with time since last conversation, with time since the person last left home and with smaller living space. Participants who reported an increase of psychotic symptoms and cognitive problems during the period of the pandemic also showed higher levels of symptoms. Although social isolation is an effective method for preventing the COVID-19 from spreading, for some individuals it is associated with an increased risk of developing psychotic symptoms.