Post-gastrectomy aspiration pneumonia (PGAP) is one type of aspiration pneumonia. Gastroesophageal reflux (GER) is thought to play an important role in the development of PGAP. Here, we report a case in which development of PGAP was prevented by an accurate diagnosis of GER. An 82-year-old male who had been treated for Parkinson's syndrome since 1995 was admitted to Hokkaido University Medical Hospital in August 2000 for evaluation of repeated pneumonia. The patient had undergone gastrectomy for the treatment of gastric cancer in 1999 and had also undergone a gastrojejunal anastomosis to correct a food-passing disturbance. Aspiration signs were not severe in a videofluorographic study for swallowing, and no indications of GER were noticed. However, scintigraphy showed repeated GER to the esophagus that occurred 16min after administration of an imaging drug. Based on these findings, a diagnosis of PGAP was made. The development of pneumonia was prevented by (1) prevention of the reflux of stomach contents into the pharynx or larynx by adjusting meal times and sleeping positions, (2) prescription of drugs to promote the rapid transfer of contents in the stomach to the small intestine, and (3) eating and swallowing training and maintenance of oral cavity hygiene.