The disappearance of the anterior vascular capsule of the lens (pupillary membrane was found to be useful in the preterm infant to estimate accurately gestational age between the twenty-seventh and the thirty-fourth weeks. Before the twenty-seventh week, the cornea was to opaque to allow good visualization of this vascular system. After the thirty-fourth week, these vessels had generally atrophied completely. One hundred infants between 27 and 34 weeks' gestational age as assessed by the Dubowitz scoring system were studied with the direct ophthalmoscope following dilatation of the pupil. Disappearance of the anterior vascular capsule was arbitrarily divided into four grades. The correlation between gestational age and the grade of anterior vascular capsule was found to be highly significant (p less than 0.001).