We investigated role of the folate-homocysteine metabolic pathway in the etiology of attention-deficit hyperactivity disorder (ADHD) due to its importance in maintaining DNA integrity as well as neurotransmission. Functional gene variants in MTR (rs1805087), CBS (rs5742905), MTHFR (rs1801133 &rs1801131), MTHFD (rs2236225), RFC1 (rs1051266), plasma vitamin B12, folate and homocysteine were analyzed. rs1805087 'A' showed strong association with ADHD. Vitamin B12 deficiency of ADHD probands (P=0.01) correlated with rs1801133 'T' and rs1805087'GG'. Mild hyperhomocysteinemia (P=0.05) in the probands was associated with rs1805087 'AA'. Probands having rs1805087 'GG' and rs1051266 'G' was more inattentive. Hyperactivity-impulsivity score revealed association with rs5742905 'TT' and rs2236225 'CC', while rs1801133 'CC' showed association with inattentiveness and hyperactivity-impulsivity. rs1801131 exhibited strong synergistic interaction with rs1051266 and rs2236225. This indicated that the folate-homocysteine pathway gene variants may affect ADHD etiology through mild hyperhomocysteinemia and vitamin B12 deficiency, factors known to be associated with cognitive deficit.