The medical records of 64 patients between 1 and 11 years old with known onset of an amblyopia-inducing condition were retrospectively reviewed to determine the upper age limit for the development of amblyopia. Thirty seven patients (group 1) developed amblyopia and 27 patients (group 2) did not. The mean patient age at the onset of the amblyopia-inducing condition was 41.0 months (2.90 SE) for group 1 and 92.3 months (4.02 SE) for group 2. The difference was statistically significant (P = .0001). No patient developed amblyopia after 73 months of age. The duration of the amblyopia-inducing condition and the type of amblyopia-inducing condition were not significantly different between the two groups. The age of the patient when exposed to an amblyopia-inducing condition is the most important determinant for the development of amblyopia. Patients 6 years or older with a normal visual system have a low probability of developing amblyopia following the onset of an amblyopia-inducing condition.