Acute retinal necrosis (ARN) is a serious condition that can impair vision. It mostly occurs in adult patients, especially those severely immunocompromised, in association with a reactivation of a herpes virus infection. We present a 4 years old patient with high risk acute leukemia, whom during a course of intense chemotherapy acquired chickenpox with visceral involvement that affected the retina, causing unilateral blindness. Varicella-zoster virus was detected by PCR in the vitreous humor, in spite of previous acyclovir treatment. The contralateral vision remained undamaged.