Background/aim: This study aimed to reveal the optimum recording time of routine electroencephalogram (EEG) for adults with epilepsy.Materials and methods: In this clinical observational study we investigated features of paroxysms that emerged in EEGs recorded for 45 min in adults with epilepsy.Results: Paroxysms were detected in 38.14% of 97 patients. The probability of occurrence of paroxysm during the first 10 min was found to be statistically significantly low in comparison to the first 30 and 45 min (respectively P = 0.004, P = 0.0001). This probability was found to increase insignificantly when comparing the first 20 min with the first 30 min (P = 0.125), but it increased significantly in comparison to 45 min (P = 0.008). On the other hand, this probability was found to increase insignificantly when comparing the first 30 min with the first 45 min (P = 0.125). The cutoff point to specify the existence of interictal epileptiform discharges in the ROC analysis was found to be ≤39 min (95% CI: 0.958-1.000), and 90% of interictal epileptiform discharges were revealed during the first 30 min of EEG recording.Conclusion: The recording time of routine EEGs for adults with epilepsy should not be less 30 min.