Menstruation is a normal, developmental event anchored in contradictory value systems. Although it demarcates a transition to womanhood, it is often associated with negative sentiments such as shame, camouflage and discomfort. Certain behavioral expectations, including avoiding sexual intercourse, also accompany menstruation. Research has generally suggested that sex does decrease during menstruation. However, not all sexual activity is suppressed during menses; both individual and relationship factors provide influence. Accordingly, this study investigated situational and relational factors associated with the day-to-day likelihood of sex and vaginal bleeding among 387 (aged 14-17 at enrollment) adolescent women. Generalized estimating equation logistic regression, in SUDAAN 9.0, was used; predictors of coitus and bleeding included recent sexual activity, past coitus/bleeding, marijuana use before intercourse and higher partner support, higher sexual interest and lower feelings of being in love. The findings highlight appropriate areas of focus for information, education and STI prevention counseling.