Knowledge of and attitudes towards dysmenorrhea among adolescent school girls were assessed in this study. A descriptive study was conducted among 200 Year 12 girls at a school in the Nugegoda Educational Division in the district of Colombo. Data collection was done by using non-probability convenience sampling. The results indicated that 84% of the study population had dysmenorrhea. Paracetamol was the drug of choice for pain relief. There was a statistically-significant (P < 0.05) association between pain and poor mental health status (66%) of the adolescent girls, but there was no significant association between pain and poor physical health (P = 0.887) and poor social health status (P = 0.395). Bathing was found to affect pain, as reported by 95% of the students. Dysmenorrhea was common among adolescent girls in our study population, and was found to affect their mental status. Health-education sessions are important to raise awareness among students of dysmenorrhea.