The effects of long term, low dosage anticonvulsant drug therapy on the vitamin D and folacin status of young children was studied. Biochemical and dietary parameters including serum calcium, phosphorous and alkaline phosphatase; serum and red blood cell folacin; serum drug concentrations; hematocrits; and dietary intakes of vitamin D and folacin were measured in seven subjects. All subjects were taking low dosages of medication. Four subjects were considered at risk for developing a folacin deficiency based on red blood cell folacin concentrations. Two of these subjects had inadequate dietary intakes of folacin. Serum calcium and alkaline phosphatase levels were within normal ranges for all subjects; two subjects had subnormal levels of serum phosphorous. Dietary intake of vitamin D was below fifty percent of the Recommended Dietary Allowance for four subjects. The data of the present study suggest that young children undergoing chronic anticonvulsant drug therapy of minimal dosage are susceptible to developing folacin deficiency especially if dietary intake of folacin is inadequate. These children do not appear to be at risk for developing vitamin D deficiency probably due to the low dosage of medication coupled with adequate sunlight exposure.