Introduction:-Polycystic ovarian syndrome is an endocrine disorder which affects the adolescent girls. It has been found through studies that it affects around 5% to 10% of women in their reproductive years. A descriptive study conducted to assess the knowledge regarding lifestyle modifications for polycystic ovarian syndrome among adolescent girls in selected school Dehradun. The objective of the study were to assess the knowledge of students regarding lifestyle modifications for Polycystic Ovarian Syndrome. To find out association of the knowledge regarding lifestyle modifications for Polycystic Ovarian Syndrome with selected demographic variables. Methodology:-The data from 60 adolescent girls of age range b/w 15-18 years was collected by using purposive sampling technique. The demographic variables of the sample in the study include age, education, religion, type of family, residence, previous knowledge, source of information, family income to life style modification for PCOS. Result:- shows that highest percentage of participants 21( 35% )of 15-16 years of age group,39( 65%) of 17-18 year of age group. In education group highest percentage 60(100%). In religion highest percentage 25(41.66%) of Hindu and 35(58.33%) of Muslim. In type of family highest percentage 29(48.34% ) of joint family and 26( 43.34%)of nuclear family , 4(6.66%) of single-parents family and 1(1.66%) extended family in residence highest percentage 57(95%) of rural area and 3(5%) of urban area family income 55(91.66%) between 10,000 to 20,000 and 3(5%) between 21,000 to 30,000 and 2(3.34%) between 31,000 to 40,000. In previous knowledge highest percentage 47(78.34%) were having no knowledge regarding of PCOS. In source of information 35 (58.34%) were having source of information from media. Majority of participation 34(57%) had poor knowledge, 21(35%) head average knowledge and 5(8%) had good knowledge. Conclusion:- The study concluded that Educating the adolescence girls regarding Polycystic Ovarian Syndrome helps girls to identify the sign and symptoms and early recognition of Polycystic Ovarian Syndrome and prevents its complication and improve infertility in future.