Background: Menstrual cycle is affected by a number of factors either positively or negatively. Disturbed menstrual cycle impacts physical, mental and social well being of women. Physical activity and exercise affect pattern of menstrual cycle depending upon its intensity. Aim: To explore the relationship of physical activity and pattern of menstrual cycle particularly dysmenorrhea and its impact on absenteeism. Study Design: Cross-sectional study Place and Duration of the Study: Department of Community Medicine, HITEC-IMS Taxila from 1st March to 31st August 2020. Methodology: One hundred and six randomly selected female undergraduate medical students of 1st to 4th year. A self-reported structured questionnaire was used to collect the data. Results: Mean age of respondents was 21.1+1.6 years. Body mass index of 47.2% respondents was normal, 26.4% were overweight and 15.1% were obese. Menstrual flow was reported light by 11.3% respondents, 74.5% had moderate and 14.2% had heavy menstrual flow. Dysmenorrhea was reported by 85% respondents, 13% had mild, 14% had moderate and 33% had severe pain during menstruation. Absenteeism was reported by 28.3% participants and was found to be associated with dysmenorrhea. Statistically significant (p<.05) association was found between physical activity and dysmenorrhea. Conclusion: Abnormalities of menstrual cycle among medical students can affect their physical well-being leading to class absenteeism. Regular and continuous physical activity can be of a great effect in improving menstrual pain and related problems. Keywords: Menstrual cycle, Dysmenorrhea, Physical activity, Undergraduate medical students