Vitamin-resistant rickets has been established as ordinary rickets which does not respond until massive doses of vitamin D are given. This study presents a series of twenty-five children and nine of ten involved parents who have been so classified. Accurate classification and diagnosis can be made by urinalysis and a few blood-chemistry studies. The most important of these are the determinations of serum calcium, serum Phosphorus, and serum alkaline phosphatase. It is now felt that the disease is far more common than has been previously reported and actually represents the most common cause of dwarfism encountered in this Clinic. It has a strong familial tendency. It may be present in varying degrees of severity and exact amount of vitamin therapy required for each individual case can only be determined a trial-and-error method. It becomes less severe after the age of epiphyseal closure, but some adults may require continued vitamin therapy.