PurposeTo present a case of iatrogenic Horner's syndrome seen together with the heterochromia in the post-thyroidectomy period.MethodsA 23-year-old female patient was admitted to our clinic with complaints of low vision in the eye and difference in eye color that developed over the past two years. In the left eye, myosis and minimal ptosis (∼1 mm) was detected, and the color of the iris was lighter than the right eye.ResultsThe pre-diagnosis of left iatrogenic Horner's syndrome was finalized after 0.5% topical apraclonidine test.ConclusionHeterochromia can be observed in iatrogenic Horner's syndrome.