It is known that the intramuscular injection of human chorionic gonadotropin (hCG) lowers the threshold for motor evoked responses (MEPs) in the first dorsal interosseous (FDI) muscle to transcranial magnetic stimulation (TMS) in humans. We describe the case of a patient with a clinically silent left-sided nasofrontal dermoid cyst who, while being treated with hCG/LH for hypogonadotropic hypogonadism, presented with simple partial seizures, ipsilateral to the cyst, with secondary generalization. Motor cortex excitability was studied by single and paired TMS and MEPs were recorded from FDI. Resting motor threshold (RMT), active motor threshold (AMT), MEP size, intracortical inhibition (ICI) and intracortical facilitation (ICF) were tested during and after suspension of hormonal therapy. RMT and AMT were lower, MEP size was larger, ICI was decreased while ICF was slightly diminished during treatment. Overall, this indicated a reduced intracortical inhibition during hormonal therapy. It is concluded that treatment with hCG/LH may favour seizure onset in the presence of potentially epileptogenic lesions such as an intracranial dermoid cyst.