Title: Attitudes and Knowledge about Oral Hygiene among Upper Grade (5th – 8th) Elementary School Student in the Area of the Town of Sinj: a Cross-sectional Study Introduction: Oral health is essential for overall health and quality of life. Oral diseases represent a significant public health problem and caries affects 90% of children and most adults. Examining children's attitudes and knowledge aobut oral hygiene and targeted education are important factors in the prevention of these diseases. Objective: The objective of this research was to examine the attitudes and knowledge of oral hygiene among primary school students of higher grades (5th grade - 8th grade) in the area of the town of Sinj. Methods: A cross-sectional survey was conducted in which students from the fifth to the eighth grade of primary schools in the area of the town of Sinj participated. Printed questionnaire was used for collecting data and it was distributed to students during their classes. The first part of the questionnaire contained sociodemographic type questions, while the second part contained questions related to attitudes and knowledge about oral hygiene. Results: 226 respondents participated in the research, of which 121 (53.54%) were girls and 105 (46.46%) were boys. The majority of respondents believe that oral hygiene is important for the overall state of health (91.6%), that clean and neat teeth are important for a better appearance (96%) and that the health of their mouths and teeth is good (97.8%). The results show that respondents have good knowledge and that there is no statistically significant difference (p < 0.05) in the level of knowledge about oral hygiene between boys and girls, in the level of knowledge between students from rural and urban areas, and in the level of knowledge of students in the fifth and sixth grades comparing to students in the seventh and eighth grades. Conclusion: Most students believe that they have adequate oral hygiene and are satisfied with the health of their teeth and mouth. Boys and girls, students from rural and urban environments and students of all grades have satisfactory knowledge of oral hygiene and a high level of awareness of the importance of oral hygiene, regardless of differences in gender, place of residence or class.