BACKGROUND Magnesium is a potential modulator of seizure activity because of its ability to antagonize the excitatory calcium influx through N-methyl-D-aspartate (NMDA) receptor which is thought to play a role in many human forms of epilepsy. When the extracellular concentration of calcium ion falls below normal, the nervous system becomes more excitable, allowing easy initiation of action potentials. Consequently, hypocalcaemia causes seizures because of its action of increasing excitability in the brain. We wanted to estimate the serum concentration of calcium and magnesium in idiopathic epilepsy patients and its co-relation. METHODS 94 cases of idiopathic epilepsy with breakthrough seizures admitted to KIMS Hospital, Hubli, meeting the inclusion criteria were considered for the study which was for 2-years’ time period. It’s a single centred, time bound and cross sectional study. RESULTS Mean serum calcium was low 8.36 ± 0.45 mg / dL and mean serum magnesium was 1.79 ± 0.28 mg / dL. 64.9 % had total serum calcium less than 8.5 mg / dL and 44.7 % had serum magnesium of < 1.8 mg / dL. 35.1 % had both low calcium and magnesium. There was significant difference in mean serum calcium with respect to number of episodes. There was no significant difference in mean serum magnesium with respect to number of episodes. CONCLUSIONS Serum calcium and magnesium levels which play a role in seizure initiation should be measured in all idiopathic epilepsy patients with breakthrough seizures as a seizure trigger. Considering the role of calcium and magnesium in the pathophysiology of seizures and by evaluating the results from the present study, breakthrough seizure could be provoked by hypocalcaemia and hypomagnesemia. Hence they may be used for the treatment of intractable seizures. KEYWORDS Calcium, Magnesium, Idiopathic Epilepsy