Background: There remains uncertainty about Covid-19 risk factors. We examined UK adults’ risk perceptions for severe Covid-19 symptoms and whether engaging in concurrent health behaviours is associated with risk perceptions. Methods: Cross-sectional analysis of data from the HEBECO study where 2206 UK adults classified potential factors (age 70+, ethnic minority, medical comorbidities, vaping, smoking cigarettes, alcohol drinking, regular physical activity, being overweight, eating unhealthy foods, using nicotine replacement therapy – NRT, lower income, poor housing, being a keyworker) as either increasing, decreasing, or having no impact on severe Covid-19 symptoms. Logistic regressions examined whether engaging in health behaviours was associated with risk perceptions after adjusting for socio-demographic characteristics, health conditions and other behaviours.Results: The great majority (89-99%) of adults classified age 70+, having comorbidities, being a key worker, overweight, and from an ethnic minority as increasing the risk. People were less sure about alcohol drinking, vaping, and nicotine replacement therapy use (17.4-29.5% responding ‘don’t know’). Relative to those who did not, those who smoked tobacco, vaped and consumed alcohol had significantly (all p<0.015) higher odds (aORs=1.58 to 5.80) for classifying these behaviours as ‘no impact’ or ‘decreasing risk’, and lower odds (aORs=.25 to .72) for classifying as ‘increasing risk’. Similarly, eating more fruit and vegetables was associated with classifying unhealthy diet as ‘increasing risk’ (aOR=1.37,1.12-1.69), and exercising more with classifying regular physical activity as ‘decreasing risk’ (aOR=2.42,1.75-3.34). Conclusions: Risk perceptions for severe Covid-19 symptoms were lower for adults’ own health behaviours, evidencing optimism bias.Implications: These risk perceptions may form barriers to changing one’s own unhealthy behaviours or make one less responsive to interventions that refer to the risk of Covid-19 as a motivating factor. Thus, in some cases risk perceptions could help sustain unhealthy behaviours and exacerbate inequalities in health behaviours and outcomes.