Purpose: Westernized eating habits have been associated with earlyage menstruation, which increases the incidence of dysmenorrhea and premenstrual syndrome among adolescent girls. We therefore surveyed changes in menarche timing and the general menstrual characteristics of adolescent girls in Seoul, Korea. Methods: We surveyed 538 teenage girls who visited our hospital between July and November 2007. Items explored included age at menarche, general menstrual characteristics, occurrence of premenstrual syndrome and treatment thereof, and an association between present dysmenorrhea and a family history of the condition. Results: Average age at menarche was 12.6 years, with 29% (n=156) subjects beginning menstruation at age 12 years. The prevalence of dysmenorrhea was 82% (n=435). The main symptoms were abdominal (53.2%) and lower back pain (34.2%), and 15.2% of girls who experienced such symptoms required medication. Present dysmenorrhea, and a family history thereof, were statistically correlated (P<0.05). In addition, 58.8% (n=316) of teenage girls had symptoms of premenstrual syndrome. The most frequent psychological symptoms were fatigue (36.4%) and nervousness (38.7%), whereas the most common physical symptom was menstrual cramps (46.5%). Most subjects (87.6%) tolerated the symptoms of premenstrual syndrome without medication; 11.4% took medicines including painkillers; but only 0.1% of subjects visited a doctor. Conclusion: The average age at menarche in Korean girls was 12.6 years, thus younger than in the past. Most teenage girls experienced dysmenorrhea and premenstrual syndrome, but few consulted a doctor. Organized treatment plans are required to manage menstrual problems in teenage girls.