Magnetic resonance imaging (MRI) is playing a growing role in the evaluation of ocular and orbital tumors. We report the case of a 26-month-old child presenting an undifferentiated retinoblastoma with a differentiated retinocytoma component in his left eye. After the eye was enucleated, we could correlate the clinicopathologic findings with the MRI scans. Both the undifferentiated retinoblastoma and the differentiated retinocytoma components could be determined on magnetic resonance imaging. Because different levels of metabolic activity within a tumor mass may influence largely T1 and T2 parameters, accurate determination of these values may be useful in determining the differentiation of a retinoblastoma, enabling a better therapeutic approach and assessment of the response to treatment.