Background: Menstruation, commonly referred to as a period or a monthly occurrence, is the regular passage of blood and mucosal tissues through the vaginal opening from the inner lining of the uterus but menstrual irregularities among adolescent may affect the normal life of adolescent girls. Some adolescent girls were suffering by menstrual irregularities like dysmenorrhea, Premenstrual syndrome, Hypomenorrhea, Amenorrhea, Oligomenorrhoea, Menorrhagia, Prolonged menstrual bleeding, Intermenstrual bleeding. The study intended to assess the pretest and posttest on knowledge of menstrual irregularities among adolescent girls in experimental and control group. The study was conducted to evaluate the effectiveness of self-instructional module on knowledge of menstrual irregularities among adolescent girls and determine the association between the level of knowledge with selected demographic variables.