As part of a study of perception of risks involved in health-related activities, 159 students (aged 16-21 years) rated 15 such activities in terms of perceived benefit, perceived risk, perceived likelihood of mishap and acceptability of present level of risk. After exclusion of 28 ex-smokers, subjects were classified into smokers vs. non-smokers, users vs. non-users of seat-belts, males vs. females and first-borns vs. later borns. There were various sex differences but few effects of birth order. Smokers tended to see a less unfavourable trade-off in terms of benefits as against risks for cigarette smoking than did non-smokers. This generalized to their ratings of pot smoking and alcoholic drinks. Non-users of seat-belts were distinguishable from users mainly in seeing greater risk and likelihood of mishap in preventive health measures such as vaccination.