Factors associated with the rickets found in children attending the Outpatients Department of Cairo Children's Hospital have been studied. All the children studied were small for their age with the rachitic children being significantly smaller than the controls. The clinical diagnosis of the disease was confirmed in 54 children by X-ray and plasma biochemistry. The best indicator of the disease was the enlarged epiphysis of the wrist and to a lesser extent that of the ankles. Some of the factors predisposing to rickets were assessed in the rachitic children and in age-matched controls. There was no difference in the nutrient intake of these two groups of children although intakes of energy, calcium and vitamin D, but not of protein, were lower than recommended dietary allowances. Although more of the rachitic children came from urban areas than the controls there were no significant differences in the environments to account for the occurrence of the disease. Factors contributing to the development of rickets are discussed with particular regard to aspects such as low body weight, low maternal vitamin D status and low calcium intakes which cause a high rate of utilization and metabolism of vitamin D.