Dementia is a rising public health concern. Feeding and nutritional problems increase as the disease progresses, affecting the clinical course and caregiver burden. While some guidelines advise against percutaneous endoscopic gastrostomy (PEG) and tube feeding in advanced dementia, conflicting evidence exists. This study aims to evaluate the nutritional status and influence of PEG feeding on the outcome and evolution of nutritional/prognosis markers of patients with severe dementia (PWSD) who underwent gastrostomy for nutritional support. We conducted a 16-year retrospective study on 100 PEG-fed PWSD with strong familial support. We evaluated the survival PEG-feeding period, safety, and objective nutritional/prognosis data on the gastrostomy day and after 3 months: Body Mass Index (BMI), Mid Upper Arm Circumference, Tricipital Skinfold, Mid-Arm Muscle Circumference, albumin, transferrin, total cholesterol, and hemoglobin. Most patients presented low values in these nutritional/prognosis parameters. No major life-threatening PEG complications were reported. The mean survival time after gastrostomy was 27.9 months (median of 17 months). Female sex, BMI recovery at 3 months, and higher baseline hemoglobin levels were associated with a reduced risk of death and increased survival time. The study concluded that, in carefully selected PWSD with strong familial support, PEG feeding can improve nutritional status and have a positive impact on survival.