ABSTRACT— Koro is an acute anxiety reaction in which the perception of decreased penis length because of hyperinvolution from intra-abdominal traction is the main feature. In an earlier study the author reported that, despite having an average length penis, Koro patients perceived smaller penis length, in both the flaccid and extended state, than did normal subjects. To examine the influence of response bias on the dysmorphic penis length perception, a longitudinal study was undertaken, in which the Draw-a-penis Test, a graphomotor projective test, was administered on the same Koro patients 3 times over 2 years. The patients showed a remarkable constancy in their perception of penis length. The dysmorphic quality of own-penis perception is discussed in relation to Koro vulnerability.