Since men view hair loss as a stressful experience, self-report of the degree of male pattern hair loss may be inherently biased and potentially affected by the degree of hair loss, age, marital status and other psychosocial factors. The magnitude of this bias can be investigated by comparing self assessments of hair loss with independent assessments by a trained observer. Subjects were recruited from initial mailings to 5000 households with at least one male resident 18 to 65 years of age within selected zip codes in the greater Dayton Ohio metropolitan area. The study sample included 273 Caucasian men, 18-50 years of age, who were selected without regard to hair loss, but excluding men self-reporting complete baldness. The degree of individual hair loss was assessed using the Norwood/Hamilton classification and a 7-point textual scale with response options ranging from a full head of hair , to I am bald . The degree of hair loss of each subject was determined independently by the subject and by the trained observer.The degree of subject-observer agreement was low for the Norwood/Hamilton classification and the textual scale for the total group and by age groups. After adjusting for the proportion of agreement due to chance, the kappa coefficient for the Norwood/Hamilton classification for the total group was 0.29. Kappa coefficients were 0.31 for subjects 18 to 30 years of age, 0.33 for subjects 30 to 40 years of age and 0.21 for subjects 40 to 50 years of age. Corresponding weighted kappa coefficients for the textual scale were 0.66 for the total group, and 0.88 for subjects 18 to 30 years of age, 0.63 for subjects 30 to 40 years of age and 0.58 for subjects 40 to 50 years of age. The low level of agreement between the trained observer and individual subjects suggests that there may be a degree of bias these men have in self-reporting their hair patterns. On average, men tended to rate themselves slightly balder than the observer. This trend was more pronounced in men with greater frontal balding than those without (42% vs. 18%). The slightly higher subject-observer agreement at the younger ages for the Norwood/Hamilton classification may be a function of a greater concern about appearance at these ages and a greater acceptance and less concern at the older ages. There was little difference among the age groups in the subject-observer agreement for the textual scale. These findings suggest that men have a poor ability in describing their hair pattern or level of hair loss compared with a trained unbiased observer. Self-perception of hair loss may be more predictive of men who will seek medical care or treatment than rater assessment.