目的 探讨左旋甲状腺素钠治疗小儿甲状腺功能减低症的疗效、安全性及合适的剂量。方法治疗组(简称L组)，用L-甲状腺素钠治疗(n=40)，对照组(简称T组)，用干甲状腺素片治疗(n=35)，观察临床表现，TSH，T3，T4及骨龄的变化。结果 两组4周症状缓解率有显著性差异，L组高于T组，(χ2=13.78，P<0.01)，TSH，T4 4周恢复时间对比，两组差异有显著性，L组高于T组，(χ2=24.75，P<0.05)，治疗组无1例出现高甲状腺素血症。结论 L-甲状腺素钠治疗小儿甲状腺功能减低症，对脑发育的改善较传统方法明显，且副作用少，值得临床推广使用。

Objective To explore the therapeutic effect, safety and appropriate dosage of Lthyroxine on child hypothyroidism. Methods In the treatment group (L Group) Lthyroxine was used (n =40), while in the control group (T Group) dry thyroxine was used (n=35). The cl inical behavior, TSH, T4, T3 and bone ages were observed. Results Significant difference in remission in the 4th week of therapy was found between the 2 groups.The L Group was significantly higher than the T Group (χ 2=13.78, P<0.01). There was a significant difference in the 4th we ek in the convalescence of TSH and T4. The L Group was higher than the T Group (χ2=24.75，P<0.05). No hyperthyroidism was found in the L Group. Conclusions Lthyroxine therapy for child hypothyroidism resu lts in significant improvement in brain development and milder side effects than tranditional treatment. Lthyroxine may be considered for clinical use.