Optimistic bias defines the tendency for human beings to underrate risk when it pertains to themselves compared with their view of risk pertaining to other people in the same conditions. The aim of this work is to investigate the optimistic bias in risk perception and health-related behaviours for three specific conditions in a young adult sample: cancer, respiratory disorders and cardiovascular diseases. Young adults showed an optimistic bias related to cancer, and to cardiovascular diseases. Our findings suggest that optimistic bias is linked to specific behavioural patterns, largely widespread in young adults, such as tobacco cigarette smoking and alcohol consumption.