Objectives: 1) to assess the existing knowledge regarding anorexia nervosa among adolescent girls in a selected schools of city. 2) To assess the effectiveness of planned teaching programme on knowledge regarding anorexia nervosa among adolescent girls in selected schools of city. 3) To associate the post test knowledge score with selected demographic Methodology: Pre Experimental One group pre test and post test research design used for the study. It was conducted over 60 adolescent girls by using Non probability Convenient sampling technique. Results: Assessment was done by using structured questionnaire on anorexia nervosa. Analysis showed that in pre test 32(53.33%) of the adolescent girls were having poor level of knowledge, 28.33% had average and 18.33% of them had good level of knowledge score, the mean score for the pretest was 6.70 ± 3.55. And in post test 1(1.67%) of the adolescent girls were having average level of knowledge, 8.33% had good, 31.67% had very good and 58.33% of them had excellent level of knowledge score, the mean score for the posttest was 19.93 with a percentage score of 79.73 %. Significance of difference between knowledge score in pre and post test of adolescent girls in relation to knowledge regarding anorexia nervosa is The tabulated value for n=60-1 i.e 59 degrees of freedom was 2.00. In addition the calculated ‘p’ values for overall knowledge regarding anorexia nervosa in adolescent girls was 0.000 which is ideal for any population. Conclusion: There was marked improvement of scores. The post test was evident as 58.33% of subjects had excellent score and 31.67% subjects had very good score. It means planned teaching programme was effective. There was no significant association between education of parents, religion, place of living and source of information about anorexia nervosa and significantly associated with age and food habits. So researcher accepts research hypothesis H1.