Background: Immune checkpoint inhibitors, such as pembrolizumab, have significantly improved outcomes in advanced non-small cell lung carcinoma. While well-tolerated in most cases, sudden onset unilateral sensorineural hearing loss is a potential complication of checkpoint inhibitors rarely reported in the literature. Case Presentation: We report the case of a patient in their 70s with a history of T3N0M0 lung adenocarcinoma treated with surgery and adjuvant chemotherapy, who experienced metastatic recurrence three years later and was placed on pembrolizumab-based systemic therapy. During maintenance monotherapy with pembrolizumab, the patient developed sudden onset right-sided sensorineural hearing loss. Systemic corticosteroid therapy led to significant improvement in the right-side hearing. Conclusion: This case highlights a rare but potentially reversible presentation of sudden onset unilateral sensorineural hearing loss in the context of immune checkpoint inhibitor therapy. Early recognition and prompt intervention with systemic corticosteroids may help preserve hearing function. Clinicians should be aware of auditory symptoms in patients receiving checkpoint inhibitors, even during long-term maintenance. Insights: Sudden-onset unilateral sensorineural hearing loss may represent a rare, immune-mediated adverse effect of pembrolizumab that can be reversible with prompt intervention.