Congenital Horner syndrome is a rare disorder that accounts for less than 5% of all cases of Horner syndrome. Like Horner syndrome in general, it consists primarily of ptosis, miosis, and anhidrosis. Congenital Horner syndrome may manifest some special features such as iris heterochromia since the sympathetic nervous system is an essential component for the development and maintenance of eye color. We present 3 cases of unilateral straight hair in association with congenital Horner syndrome in which the patients had straight hair ipsilateral to the Horner syndrome, whereas on the contralateral side, it was curly, and we discuss possible mechanisms for this phenomenon.