Menstrual irregularities is the one of the common problem among adolescent girls. Particularly girls in their teens or early twenties. Over weight, lifestyle patterns, eating habits and body mass index are related to the cause for the number of cases with menstrual irregularities. The present study was conducted among the adolescent girls to assess the relationship between the body mass index and menstrual irregularities at SMVNC at puducherry. A quantitative research approach with descriptive research design was selected for this study. The study samples was selected by quota sampling which comprises of 75 adolescent girls from 1st year B.sc nursing to 4th year B.sc nursing. The menstrual irregularities were assessed among the adolescent girls and their body mass index was calculated. The findings of the present study reveals that there is a relationship between the body mass index and menstrual Irregularities among the adolescent girls.