INTRODUCTION: Treatment-resistant depression (TRD) is a serious and debilitating psychiatric disorder that frequently affects older patients. Esketamine nasal spray (ESK-NS) has recently been approved as a treatment for TRD, with multiple studies establishing its efficacy and tolerability. However, the real-world effectiveness, tolerability, and safety of this treatment in older adults is still unclear. OBJECTIVES: To evaluate the efficacy and tolerability of ESK-NS in older subjects with TRD. METHODS: This is a post-hoc analysis of the REAL-ESK study, a multicenter, retrospective, observational study. Participants here selected were 65 years or older at baseline. The Montgomery-Åsberg Depression Rating Scale (MADRS) and the Hamilton Anxiety Rating Scale (HAM-A) were used to assess depressive and anxiety symptoms, respectively. Data were collected at three-time points: baseline, 1 month after the start of treatment (T1), and 3 months after treatment (T2). RESULTS: The sample included older adults with TRD (n = 30). MADRS and HAM-A values decreased significantly at T1 (T0 versus T1: p <0.001, Cohen's d = 0.840) and T2 follow-ups (T0 versus T2: p <0.001, Cohen's d = 1.419). At T2, 53.3% of subjects were responders (MADRS score reduced ≥50%), while 33.33% were in remission (MADRS<10). ESK-NS-related adverse effects were in order of frequency dizziness (50%), followed by dissociation (33.3%), sedation (30%), and hypertension (13.33%). Six out of 30 participants (20%) discontinued treatment. CONCLUSIONS: Our findings provide preliminary evidence of ESK-NS effectiveness in older adults with TRD, a highly debilitating depressive presentation. Furthermore, we observe high levels of treatment-emergent adverse events, which, in the majority of instances, did not require treatment suspension.