In the United States, 50% of all retinoblastoma cases are diagnosed after the observation of leukocoria by a family member or primary care physician. However, leukocoria produced by retinoblastoma lesions can often be missed by direct ophthalmoscopic examination through an undilated pupil. The purpose of this study is to demonstrate the utility of pupillary dilation for the detection of leukocoria in suspected cases. Seven patients (10 eyes), aged 2 days to 20 months, with retinoblastoma were examined for leukocoria using a direct ophthalmoscope with the pupils first undilated and then after pharmacologic dilation with 0.5% cyclopentolate and 2.5% phenylephrine. Leukocoria was detected by direct ophthalmoscopy on undilated examination in 3 of 10 eyes (30%). In contrast, leukocoria was observed after pupillary dilation in 10 of 10 eyes (100%). The retinoblastoma lesions, from 2 to 10 mm in diameter, were located within the posterior 45 degrees of the retina. Pupillary dilation is a safe and effective tool that can enhance the ability of the examiner to detect leukocoria. Dilation may afford early diagnosis and treatment, and therefore should be considered on patients in whom the diagnosis of retinoblastoma is entertained.