AIM: To establish normative values for the anterior segment in premature infants in relation to postconceptional age and birth weight. METHODS: Anterior segments were measured in 39 premature infants, 25 to 39 weeks' gestational age by use of ultrasound biomicroscopy and a muscle hook with topical anaesthesia. RESULTS: Anterior chamber depth, trabecular-iris angle, angle opening (trabecular-iris) distances at 250 and 500 microns from the scleral spur, and the thickness of the thickest part of the iris showed linear increases in relation to postconceptional age and birth weight. CONCLUSIONS: Ultrasound biomicroscopy is a powerful tool for obtaining precise images and measurement of the anterior segment in preterm neonates. Normative values were established for anterior segment dimensions in relation to postconceptional age and birth weight.