A 2-month-old boy presented with an irregular left pupil. Over the course of 3 months, progressive pupil ovalization, corectopia, and ballooning of the thinned superior iris tissue caused obstruction of the visual axis. Because of concern for deprivational amblyopia, a sectoral pupilloplasty and sphincterotomies were performed, restoring pupil shape and clearing the visual axis. On postoperative examinations, the pupil remained round, the visual axis clear, and visual acuity of the left eye improved. Findings and clinical course suggested the diagnosis of idiopathic tractional corectopia, a rare congenital disorder of unknown cause that may lead to isolated unilateral progressive corectopia and visual axis obstruction. Patients should receive regular follow-up examinations.