One hundred fifty-four cases of infantile esotropia and acquired esotropia surgically treated before the age of seven were followed for a minimum of five years. We found 44% of infantile esotropia and 60% of acquired esotropia were converted to phoria with 20% having postoperative exotropia. Eight to 10 years of age seemed to be the turning point from esotropia to exotropia. Spontaneous decrease of accommodative convergence with age seemed to be the most important causative factor in relation to secondary exotropia. Long-term follow-up revealed the residual angle of deviation decreased with time and undercorrected esotropia resolved spontaneously. Therefore, it is the responsibility of the surgeon to encourage his patients to return regularly for follow-up visits even ten years after surgery for possible spontaneous change of deviation.