Higher rates of reported morbidity among women are sometimes attributed to lower thresholds among women for experiencing and reporting symptoms. Gender differences in the perception of signs and symptoms of minor illness were examined on data from the MRC Common Cold Unit. Volunteers assessed the presence and severity of colds at the end of their stay in the Unit, using the same two measures as a trained clinical observer (all ratings were double blind). Even after adjustment for other variables, men were significantly more likely to 'over-rate' their symptoms in comparison with the clinical observer than were women. These data, and recent analyses from elsewhere, suggest that rather than artefactually exaggerating gender differences in morbidity, differing thresholds for perceiving and reporting symptoms may produce underestimates of gender differences in morbidity.