The purpose of this study is to evaluate the relationships between serum free fatty acids (FFA) and zinc, and attention deficit hyperactivity disorder (ADHD). Forty eight children with ADHD (33 boys, 15 girls) were included in the patient group and 45 healthy volunteer children (30 boys, 15 girls) constituted the control group. The mean serum FFA level in the patient group was 0.176 +/- 0.102 mEq/L and in control group, 0.562 +/- 0.225 mEq/L (p < .001). The mean serum zinc level of patient group was 60.6 +/- 9.9 mu g/dl and that of the control group, 105.8 +/- 13.2 mu g/dl (P < .001). A statistically significant correlation was found between zinc and FFA levels in the ADHD group. These findings indicate that zinc deficiency may play a role in aetiopathogenesis of ADHD. Although we observed decreased FFA levels in ADHD cases, it is necessary to determine whether this condition is a principal cause of ADHD or is secondary to zinc deficiency.