The assesment of skeletal maturation has been considered an important feature of peripheral thyroid hormone action. The surface of the epiphysis of the knee (SE) was calculated, following the method described by Rochiccioli et al, in 30 infants with NH detected in different screenings programs. The anatomical situation of thyroid gland was demonstrated by 131I or 99mTc scintigraphy. 25 had athyreosis (Group I) and 5 ectopics glands (Group II). The SE of the distal femoral epiphysis CFD) in all hypothyroids was 10.27 ±2.08 mm2 and that of proximal epiphysis of tibia (TP) was 4.48±1.7 mm2 (Normal values= FD=26.2±0.79 mm2; TP2 13.5±0.38 mm2). Group I=FD=8.01±1.6 mm2, present in 15/25; TP=2.3±1.08 mm2 present in 4/25. Group II FD=21.3±1.08 mm2, present in 4/5, TP=15.9±7.1 mm present in 4/5. There was significant difference in the 2 group in FD (p<0.02) and TP (p<0.05). No correlation was observed with growth and height attained at 2 and 4 years of age. T4 and T3 serum levels were higher in infants with ectopic glands than athyreosis p<0.005. In conclusion:1)the epiphysis of the knee was present in 63% of infants with NH, 2)The SE of both epiphysis was smaller in hypothyroids than in normals, 3)FD appears in 60% of infants with athyreosis and 80% with ectopic glands: TP only in 16 and 80% respect iveLy, 4)SE was higher in infants with ectopic glands than in athyreosis. Thus, the calculation of SE of the knee may be considered as a criterion of duration and severity of NH and may be useful to judge the onset and degree of thyroid deficiency.