To report the association between herpes simplex virus (HSV) and iris atrophy with pupillary dilation.Retrospective case series.Patients with a clinical diagnosis of HSV keratouveitis seen between November 1993 and April 1994 in a single university uveitis clinic. There were 6 women and 7 men, aged 17 to 69 years (mean age 44.4 years).Patient information was collected, including history and medications used, and a complete ophthalmologic evaluation was performed, with careful documentation of iris detail and pupillary size.Thirteen of 13 patients demonstrated some degree of iris atrophy; 9 of 13 had pupillary dilation on the affected side despite not being on dilating drops.Iris atrophy and pupillary dilation in a patient with unexplained anterior uveitis suggests the diagnosis of HSV keratouveitis.