The records of 128 children, whose birth weight was below 2500 g and who were seen again at the ages of 13-14 years, were analyzed. Owing to the knowledge of the data of the last maternal menses in 115 cases, they could be separated in at-term dysmature, premature dysmature and true premature infants. The comparison between the 3 groups led to the following differences: On average, there is little difference between true premature infants and normal neonatal population, on both somatic and psychological points of view. Physical development is less satisfactory in at-term dysmature infants. If their median of I.Q. is close to normal, high intellectual abilities are rare and mental deficiency more frequent. In the physical, auditory, visual and psycho-motor fields, premature dysmature infants are the most underpriviliged.