Feedback-related negativity is an event-related brain potential elicited by negative feedback. Its properties make it a valuable tool for the assessment of cognitive-affective processes that are involved in feedback and reward processing. The present study sought to determine the minimum number of trials that are required to obtain a reliable FRN component using a simple gambling paradigm. Three independent groups of young participants and one group of old participants were used. In the experimental conditions with healthy young controls, 20 trials were sufficient to measure the optimal FRN amplitude. In older participants, 50 trials were needed to obtain a reliable FRN. Whereas 20 trials would be enough to ensure a reliable FRN component in studies with nonclinical samples, the number of trials needed in clinical and cognitively impaired populations has to be determined based on the signal-to-noise ratios and the characteristics of the signals recorded.