An HPLC procedure for the determination of lamotrigine (LAM) simultaneously with other antiepileptic drugs, primidone (PD), phenobarbital (PB), phenytoin (DPH), carbamazepine (CMZ), and two active metabolites 2-phenyl-2-ethyl-malonamide (PEMA) and 10,11-dihydro-10,11-epoxycarbamazepine (EPO) was developed and validated. The method involves an ordinary RP system and a liquid-liquid extraction. The mobile phase consisting of water/ACN/methanol/triethylamine in the ratio 72:23:5:0.1 with pH 7.0 was selected as the best one after the assays testing both pH and triethylamine contents. UV detection was carried out at a wavelength of 220 nm and the whole analysis took 15 min. The method was linear in the range of 0.5-25 mg/L for PEMA and LAM; 1.25-25 mg/L for PD and CMZ; 0.625-12.5 mg/L for EPO; 1.5-60 mg/L for PB; and 1.25-50 mg/L for DPH, respectively. Within-day CV% and between-day CV% were within 10%. The developed HPLC method can be used for routine therapeutic drug monitoring both in children and adults.