Maternal folic acid supplementation has been suggested to play a role in the prevention of nonsyndromic orofacial clefts, i.e., cleft lip Ϯ cleft palate. Using a case-control design, we investigated vitamin-dependent homocysteine metabolism in 35 mothers with nonsyndromic orofacial cleft offspring and 56 control mothers with nonmalformed offspring. A standardized oral methionine loading test was performed, in which fasting and afterload plasma total homocysteine, serum and red-cell folate, serum vitamin B12, and whole-blood vitamin B6 levels were determined. We found that both fasting (P Ͻ 0.01) as well as afterload (P Ͻ 0.05) homocysteine concentrations were significantly higher in cases compared to controls. Hyperhomocysteinemia, defined by a fasting and/or afterload homocysteine concentration above the 97.5th percentile, was present in 15.6% of the cases and in 3.6% of controls (odds ratio, 5.3 (1.1-24.2)). The median concentrations of serum (P Ͻ 0.01) and red-cell (P Ͻ 0.05) folate were significantly higher, and vitamin B6 concentrations appeared to be significantly lower (P Ͻ 0.05), in cases compared with controls. No significant difference was observed between groups for vitamin B12. These preliminary data offer evidence that maternal hyperhomocysteinemia may be a risk factor for having nonsyndromic orofacial cleft offspring.