Health risk judgments are not merely based on risk statistics but also on the ease with which hypothetical events are imagined. We explored the effects of scenario information as opposed to frequency information on susceptibility perceptions regarding Chlamydia and HIV. Results showed that participants felt more susceptible to Chlamydia after reading frequency information. Scenario information only seemed to affect feelings of susceptibility in participants with no intimate relationship. No effects on perceived susceptibility for HIV were found. Results are discussed in terms of severity of the disease and defensive reactions.