Background <p>Posterior reversible encephalopathy syndrome is a rare neurological disorder typically associated with hypertension, cytotoxic agents, or supratherapeutic immunosuppressant levels. We report what appears to be the first documented case of posterior reversible encephalopathy syndrome in a bilateral lung transplant recipient occurring with subtherapeutic tacrolimus levels.</p> Case presentation <p>A 59-year-old white male with prior bilateral lung transplantation and multiple risk factors, including sepsis, corticosteroid use, and acute kidney injury, presented with sudden bilateral cortical blindness and seizures, initially concerning for stroke. Tacrolimus levels were subtherapeutic. Rapid diagnosis of posterior reversible encephalopathy syndrome was made using computed tomography stroke perfusion imaging. Intensive blood pressure control and substitution of tacrolimus with cyclosporin led to complete neurological recovery.</p> Conclusion <p>This case highlights the multifactorial nature of posterior reversible encephalopathy syndrome and the need for vigilance even when immunosuppressant levels are subtherapeutic. Early recognition and timely management can prevent irreversible neurological injury, with important implications for transplant care and immunosuppressive therapy monitoring.</p>