The hypothyroidism is a frequent endocrinopathos. The authors report a retrospective study of 67 cases gathered at pediatric department of Sfax, during 23 years. 40 boys and 42 girls aged from 1 to 164 months, with an average of 55 months old children. The most clinical symptoms have been the dysmorphic syndrome (81.17%), Huge tongue (59.75%), the T3 is low in 30.48%, the FT4 or the T4 is low in 79% and the TSH is high in 84.14%. All the patients have benefitted a treatment based on thyroidian extract from 1977 to 1984, and since 1985 it was based on L. Thyroxin. The neuropsychiatric prognosis satisfactory in 72% and 28% have a mental delay and 56% a delay in growth. The authors insist on the necessity of doing an early diagnosis and treatment which is the only way and issue leading to a favorable neuropsychiatric evolution.