Background : Illness is one of the major problems caused by infection that happened in school period. Among many factors, infection can be lead by lack of student’s knowledge about Hand Hygiene. Hand hygiene is a process to clean both hands precisely by doing the hand was or the hand rub process. Parents also a vital agent that taught and supported this activity to their kids. Unfortunately there’s so little amount of researched done before to know how’s the effect of hand washing to the number of illness in school area. Purpose : Examining the Relationship between Knowledge of Hand Hygiene in Students and Student’s Parents on Morbidity in SMA Negeri 11 Yogyakarta. Method : This study using a cross sectional method with the number of sample involved are 87 students of X and XII grade and also their parents. Sample was randomly taken from finite random sampling formula. Hand hygiene knowledge was measured with a questioner that already tested the validity and the reliability before. Logistic regression was used for statistic analysis. The study was held in SMA Negeri 11 Yogyakarta, from April-September 2016. Result : None of the result from bivariate statistic analysis shown any correlation between hand hygiene knowledge of students and their parents with the number of illness that happened in school area. For the multivariate statistic analysis show that low rate of knowledge about hand hygiene from the students not correlated with the number of illness that happened (OR=0,334; 95% CI: 0,088-1,265). Low rate of knowledge about hand hygiene from the student’s parent show a low score of correlation with the number of student’s illness in school (OR=6,951; 95%CI: 1,842- 26,228). The correlations were analyzed from class, age and gender to be analyzed. Social class showed a higher rate of illness than science. The older the student’s gets the higher chances to get the illness. Conclusions : There is a correlation between knowledge of hand hygiene of parents with the illness of students in SMA Negeri 11 Yogyakarta, but there is no relation between knowledge of hand hygiene with the incidence of illness in SMA Negeri 11 Yogyakarta students.