Psoriasis is a chronic inflammatory disorder that manifests as cutaneous lesions and/or systemic conditions that can negatively affect patient quality of life. Psoriasis is incurable and standard of care consists of symptom management. We report the case of a 47-year-old male with a 28-year history of plaque psoriasis that underwent a 13-day, medically supervised, water-only fast, which coincided with a clinically meaningful reduction in the severity of his psoriatic lesions. After the water-only fast, the patient followed an exclusively whole-plant-food diet without medications and at the two-month, follow-up visit there was continued improvement with no new plaque formation. This case provides a basis for further inquiry into prolonged water-only fasting followed by an exclusively whole-plant-food diet in the treatment of severe plaque psoriasis.