Low birth weight infants are a heterogenous group of babies with medical risks that may vary according to gestational age. The degree of prematurity should be assessed using non-invasive valid methods. The purpose of this study was to assess the validity of four most commonly used methods for the assessment of gestational age in two groups of 60 appropriate for date pre-terms and 29 small for date babies. Our results support the use of prenatal assessment of gestational age by maternal history and early ultrasonography in afd-infants, the use of the examination of the anterior vascular capsule of the lens in afd and sfd infants and physical criteria rather than neurologic criteria when using the Ballard score.