Introduction: Menstrual irregularities in adolescent girls are rapidly increasing worldwide. Exposure to endocrine-disrupting chemicals such as plastics including Bisphenol A (BPA), Phthalates and Polyvinyl chloride (PVC) are potential environmental toxins contributing to hormonal imbalance and irregular menstrual cycles. Aim/Objectives: We examined the association between plastic usage and menstrual cycle characteristics among Adolescent girls aged 15–19 years who were participating in a questionnaire-based cohort study under the program on reproductive health awareness in adolescent girls. Materials and Methods: A case-control study of 360 girls was conducted in 2016 and 2019 in a school in Rajasthan, India. We used self-reported information through a questionnaire to assess the association of irregular menstrual cycles (≤25 days and ≥35 days) with extent of plastic usage categorized here as medium and high. Results: The study cohort had a high prevalence of irregular menstrual cycles (40.8%). Heavy plastic exposures increased the chances of getting irregular periods significantly. Girls with irregular menstrual cycles had more prevalence of hair fall, acne, acanthosis nigricans, and abnormal hair growth/hirsutism. Girls with family history of diabetes and CVD were more susceptible to develop irregular menstrual after heavy usage of plastics. Both medium and high exposures to plastics were associated with abnormal hair growth/hirsutism (p