Four studies were conducted with college student subjects to examine: (1) perceptions of susceptibility to health and safety risks; (2) factors that subjects see as important in determining their susceptibility; and (3) subjects' actual standing on objective risk factors. Subjects were generally unbiased about hereditary risk factors and were even somewhat pessimistic about environmental risk factors. Their views of their own actions and psychological attributes, however, were excessively optimistic. Few acknowledged actions or psychological attributes that increased their risk. This pattern of findings helps to explain why risks thought to be controllable (i.e., preventable by personal action) are likely to evoke unrealistic optimism about susceptibility. Family histories of health problems were incorporated into judgments of susceptibility, but, except for smoking, correlations between behavioral risk factors and judgments of susceptibility were surprisingly weak. Self-esteem enhancement is suggested as a motive that could explain many of the present findings. Several recommendations are offered for health campaigns that seek to produce more realistic perceptions of susceptibility to health and safety problems.