A simple HPLC method was developed and validated for quantitation of lamotrigine and its related substances which may coexist in solid pharmaceutical dosage forms. The HPLC separation was achieved on a C18 mu-Bondapack column (250 mm x 4.6 mm) using a mobile phase of acetonitrile-monobasic potassium phosphate solution (35:65, v/v) containing orthophosphoric acid to adjust pH to 3.5 at a flow rate of 1.5 ml/min. The UV detector was operated at 210 nm, and column temperature was adjusted at 40 degrees C. The method was validated for specificity, linearity, precision, accuracy, robustness and limit of quantitation. The degree of linearity of the calibration curves, the percent recoveries of lamotrigine and related substances, the limit of detection and quantitation, for the HPLC method were determined. The method was found to be simple, specific, precise, accurate, and reproducible. The method was applied for the quality control of commercial lamotrigine tablets to quantify the drug and its related substances and to check the formulation content uniformity.