This paper attempts to understand the experience of menstruation in the socio-cultural context of an urban Indian slum. Observations were gathered as part of a larger study of reproductive tract infections in women in Delhi, using both qualitative and quantitative methods. The qualitative phase consisted of 52 in-depth interviews, three focus groups discussions and five key informant interviews. In the quantitative phase inferences were drawn from 380 respondents. Mean age at menarche was 13.5. Onset of menarche is associated with physical maturity and the ability to marry and reproduce. However, a culture of silence surrounds menarche, an event which took the women interviewed almost by surprise. Most were previously unaware that it would happen and the information they were given was sparse. Menstruation is associated with taboos and restrictions on work, sex, food and bathing, but the taboos observed by most of the women were avoidance of sex and not participating in religious practices; the taboo on not going into the kitchen, which had been observed in rural joint households, was not being observed after migration from rural areas due to lack of social support mechanisms. There is a clear need to provide information to young women on these subjects in ways that are acceptable to their parents, schools and the larger community, and that allow them to raise their own concerns. Education on these subjects should be envisaged as a long-term, continuous process, beginning well before menarche and continuing long after it.