Nutritional rickets remains a common child health problem in Turkey and many other developing countries. Although vitamin D deficiency is accepted as the basic problem underlying the disease, others postulate that a deficiency of dietary calcium, rather than vitamin D, is often responsible for the nutritional rickets in sunny countries. We conducted a placebo-controlled study to determine the best treatment regimen for nutritional rickets in children residing in lower socioeconomic regions of a sunny city, Istanbul. Forty-two infants (aged 6-30 months) with rickets were divided into three groups and included in the study. In a randomized fashion vitamin D (300 000 units, intramuscularly), calcium lactate (3 g daily) or a combination of vitamin D and calcium were given to the children. Alkaline phosphatase, calcium, albumin, ionized calcium and phosphorus levels were measured each week. X-ray examinations of the left wrist and left knee were undertaken at the beginning of the study and were repeated at the 2nd and 4th weeks and were scored in order to assess the response to treatment. Treatment produced an increase in serum calcium and a decrease in alkaline phosphatase concentration in all three groups, but the most important increase was reached in the vitamin D plus calcium group. We conclude that vitamin D deficiency appears to be the primary etiologic factor of rickets in our study group, but a better response to treatment with vitamin D or in combination with calcium was obtained than to treatment with calcium alone.