All eighth-grade pupils of secondary schools in a Finnish town completed questionnaires 3 times during a 17-month follow-up. A total of 935 girls were included in the study. The mean age of the girls at the start of the study was 14.5 years. The results showed that there were differences in psychosomatic symptoms, dating, and alcohol use by age of menarche. However, the results suggested that the differences by age of menarche were largely associated with pubertal development as such. After controlling for time since menarche, the impact of timing on psychosomatic symptoms was demonstrated only at the beginning of the study, not later. Differences in behavior also seemed to be related to pubertal development rather than timing. Differences in symptoms by age of menarche remained after controlling for dating and alcohol use.