Electroconvulsive therapy (ECT) remains the most effective therapy in treatment-resistant depression. However, the safety of ECT has been consistently questioned, particularly among elderly patients. We assessed the efficacy and safety of ECT in patients before and after 65 years old. The study was conducted between 2015 and 2018 and included 91 patients (61 under and 29 over 65 years old) with major depression undergoing ECT. The Hamilton Depression Rating Scale was used to evaluate efficacy. Cognitive functions were assessed using: MMSE, RAVLT, Trail Making Test, Stroop Test and Autobiographical Memory Interview-Short Form. ECT was more effective in older patients as compared to younger (p < 0.001). No serious adverse events were observed in either group. Increased blood pressure and arrhythmias were more common in the older compared to the younger group (p = 0.044 and p = 0.047, respectively), while disturbances of consciousness did not differ between groups (p = 0.820). Most of the cognitive functions remained unchanged compared to baseline, whereas the outcomes of MMSE, RAVLT and Stroop tests showed greater improvements in the older compared to the younger group (all p < 0.05). The decline in the retrieval consistency of autobiographical memory was more pronounced in the younger group (p = 0.024). ECT is a highly effective, safe and well-tolerated method of treating depression regardless of age.