Perihepatitis, including Fitz-Hugh-Curtis syndrome, is an uncommon, chronic manifestation of pelvic inflammatory disease usually affecting premenopausal women. It causes right upper quadrant pain due to inflammation of the liver capsule and adhesion of the peritoneum. Since delayed diagnosis of Fitz-Hugh-Curtis syndrome can lead to infertility and other complications, physical examination findings need to be investigated to predict perihepatitis in the early stages of the disease. Here, we hypothesized that perihepatitis is characterized by increased tenderness and spontaneous pain in the right upper abdomen when the patient is placed in the left lateral recumbent position (we termed this indication the "liver capsule irritation sign"). We examined the patients physically for the presence of this liver capsule irritation sign for an early diagnosis of perihepatitis. We report the first two cases of perihepatitis due to Fitz-Hugh-Curtis syndrome in which the liver capsule irritation sign observed during the physical examination was used for diagnosis. The liver capsule irritation sign is caused by two mechanisms: first, the liver falls gravitationally into the left lateral recumbent position, which makes the liver easier to palpate; and second, the peritoneum is stretched and thus stimulated. The second mechanism is that the transverse colon running around the right upper abdomen slumps gravitationally when the patient is in the left lateral recumbent position, allowing for direct palpation of the liver. The liver capsule irritation sign can be a useful physical finding, suggestive of perihepatitis due to Fitz-Hugh-Curtis syndrome. It may also be suitable in cases of perihepatitis caused by factors other than Fitz-Hugh-Curtis syndrome.