What is the most likely cause of abdominal pain in a young woman with tenderness in the right lower quadrant and a negative pregnancy test?

The most likely cause of abdominal pain in this scenario is acute appendicitis. In young women, right lower quadrant pain can often be attributed to gynecological issues, but given that the pregnancy test is negative, other causes need to be considered.

Acute appendicitis typically presents with localized tenderness in the right lower quadrant, and it can occur in both males and females, making it a strong contender especially in a young woman. The clinical features of appendicitis often include not just pain but also possible nausea and vomiting, with the pain usually starting around the umbilical area and then localizing to the right lower quadrant. This pattern of pain is consistent with appendicitis.

While pelvic inflammatory disease and ovarian cyst rupture can also cause right lower quadrant pain in women, these conditions may involve other symptoms such as abnormal vaginal discharge, fever, or irregular menstrual bleeding, which are not mentioned here. Gastroenteritis would more likely present with diffuse abdominal pain and associated symptoms such as diarrhea or vomiting but would not typically localize specifically to the right lower quadrant. Therefore, acute appendicitis stands out as the most likely diagnosis given the described symptoms and the negative pregnancy test.