The purpose of this research is to explore some aspects of "unrealistic optimism" during adolescence: 1) if the amount of optimism varies according to the attributes of the events or behaviors; b) age and gender differences in optimism and c) the role of some personal attributes as determinants of optimistic biases (self-esteem, health locus of control, values and sensation-seeking). The sample includes 200 adolescents, male and female, of two age groups (15 and 18 years old). Results show that adolescents underestimate personal susceptibility to different risks, and that this tendency is more pronounced for certain events/behaviors. Age is generally nonsignificant, but optimism is stronger among female subjects. Among the personal attributes considered, sensation-seeking appears a strong determinant of optimistic beliefs at a general level, whereas the causal role of the other variables depends on the particular event/behavior.