Retinoblastoma is a malignant (cancerous) tumor that occurs in the eye. It arises in the part of the eye known as the retina, which is located along the back wall of the inside of the eye.

Retinoblastoma is relatively rare, occurring in one in 15,000 to 16,000 births and often is diagnosed in children who are less than 2 years of age. It more commonly occurs in only one eye.

There are two forms of retinoblastoma: sporadic and heritable. Of retinoblastoma cases, 60 percent are sporadic.  There is strong evidence that when retinoblastoma occurs in both eyes, there is a hereditary factor. When an individual has both eyes affected (bilateral retinoblastoma), his or her children have approximately a 45 percent chance of developing retinoblastoma themselves.