A 19-year-old woman has painful ulcers on the labial mucosa and buccal mucosa of 4 days duration. she has had similar ulcers on previous occasions, and each time the lesions healed in approximately 7 days. the best diagnosis is

Based on the age and demographic, the best diagnosis given the facts is genital herpes. The recurrence of the ulcers in the labial region are indicative of a chronic viral infection. The odds of genital herpes from a single unprotected exposure are quite realistic at approximately 1 in 1000 which support assertion that herpes is the best diagnosis.

The best diagnosis is aphthous ulcers.

The description above is fits what aphthous ulcers are. They might occur several times a year, and always last about 7 days total. These are painful ulcers which may appear in a person's mouth a couple of times a year and are a minor nuisance.