The present study sought to measure the accuracy of symptom reporting in patients with asthma by calculating the difference between a subjective rating of illness severity and an objective test of lung function (forced expiratory volume in 1 second). At issue was the hypothesis that self-reported “symptom amplification” or sensory awareness accounts for differences in the accuracy of symptom reporting. Spirometric examination was performed, and psychological tests of symptom amplification, emotional distress, and neuroticism were administered. Participants consisted of 42 consecutive patients seeking medical treatment of asthma. The disparity between symptom perception (assessed by a Borg scale) and a corresponding measure of lung capacity allowed us to identify patients who overreported their symptoms (amplifiers) along with those who underreported them (minimizers). After controlling for the effects of sex and psychological distress, a self-report measure of symptom amplification explained 15% of the variability in reporting accuracy. Related constructs such as somatization and neuroticism could not explain differences in reporting ability.