Background: Normal skeletal development and adult bone maintenance requires normal level of thyroid hormones. Growth arrest, delayed bone maturation, and epiphyseal dysgenesis are fundamental result of hypothyroidism in children.    
Aim of the work: To detect the effects of hypothyroidism and thyroxin treatment on the postnatal development of lumbar vertebrae in albino rats.
 Materials and Methods: Sixty adult female rats were randomly subdivided into three equal groups; control group (received distilled water), carbimazole-treated group (received carbimazole in a dose of 6 microgram/gram body weight daily orally from 10^th gestational day till the day 21 postnatally then carbimazole administration was continued to pups until the end of 8^th week postnatally) and carbimazole+thyroxin treated group (received carbimazole on 10^th gestational day in a dose of 6 microgram /gram body weight orally and thyroxin at birth in a dose of 10 microgram/kg/day orally and the administration of both drugs was continued until the day 21 postnatally then the administration was further continued to pups until the end of 8^th week postnatally). The offsprings at ages (newborn, two weeks and eight weeks) anesthetized, sacrificed, their lumbar vertebrae were manibulated for histological examination. Morphometric and statistical studies were performed.  
Results: The lumbar vertebrae markedly affected by hypothyroidism especially the proliferating zone and the collagen component of the matrix. Morphometric results revealed highly-significant decrease in the thickness of the epiphysis in hypothyroid rats. Most of these changes reverted by giving thyroxin.
Conclusion: Vertebral column growth is markedly affected by hypothyroidism and thyroxin replacement has a protective role.