Aim: A study to assess the relationship between Body mass index and menstrual irregularities among female students studying at Desh Bhagat University, Mandi Gobindgarh, and Fathegarh Sahib. Method: The descriptive co relational study was conducted in Desh Bhagat University, Mandi Gobindgarh. Data was collected from 287 female students studying at Desh Bhagat University, Mandi Gobindgarh. Out of them, 200 female students had menstrual irregularities. Self structured checklist was used to assess the menstrual irregularities and to check BMI weighing machine and measuring tape was used. Result: The occurrence of menstrual irregularities was (69%) among female students. Most of the female students had mild degree of menstrual irregularities (81%) and had normal BMI (71%) Coefficient of correlation showed that BMI had moderate degree of positive correlation with Menometorrhagia and BMI had high degree of negative correlation with Hypomenorrhea. Chi square showed that there is association between menstrual irregularities with selected demographic variables (Age Educational level, marital status, Family income and Age at menarche) and is there is association between BMI With selected demographic variables (Age Educational level, Marital Status, Duration of bleeding during menstrual cycle in days). Conclusion: Obesity is one of the important causes of irregular menstrual cycles. Hence there is a role for lifestyle modifications.