Background of the study: The normal menstrual cycle is about four weeks long, and often follows the phases of the moon. Its length varies from three to seven days, but is usually consistent. However, girls and teenagers who menstruate are usually irregular. For most women, a normal menstrual cycle ranges from 21 to 35 days.1 However, 14% to 25% of women have irregular menstrual cycles, meaning the cycles are shorter or longer than normal; are heavier or lighter than normal; or are experienced with other problems, like abdominal cramps. Irregular cycles can be ovulatory, meaning that ovulation occurs, or anovulatory, meaning ovulation does not occur. Objectives: To assess the pre-test knowledge on menstrual irregularity among adolescent girls in selected high school. To assess the post test knowledge on menstrual irregularity among adolescent girls in selected high school. To evaluate the effectiveness of structure teaching programme on knowledge regarding menstrual irregularity among adolescent girls in selected high school. To find out the association between the pre-test knowledge score with selected demographic variables. Methods: The study involved evaluative approach and one group pre and post test only without control group research design with simple random sampling technique. And data has collected through structured knowledge quesionnarie. Results: As per the study findings 3.33% adolescent girls had inadequate knowledge, 76.67% had moderate level of knowledge and 20% had adequate level of knowledge regarding menstrual hygiene. In all demographic factors age in years of adolescent girls, educational status of mother, educational status of father, number of elder sisters statistically not associated with their pre-test knowledge score and there is association of pre test knowledge score with religion, type of family, monthly family income, age of menarche and source of information. The present statistically shows the enhancement of 11.07 in mean, 0.7 in standard deviation with the ‘z‘ value of 29.19 at 0.05 level of significance. It was inferred that there was significant enhancement in knowledge score after structure teaching program.

Keywords: Adolescent; Menstrual irregularity; Chi-Square Test; Knowledge; Structure teaching programme.