Osteoporosis is a growing chronic health problem that could result in mortalities and poor living quality. This study aimed at assessing the awareness of adults in Riyadh about this disease and its associated factors as well as compare KAP levels of men and women. A cross sectional study including 505 participants was conducted in several malls of Riyadh city during March 2012, selected by stratified random sampling technique. Self-administered questionnaire was used for data collection. 86% of the participants had heard of osteoporosis. Media was the main source for Participants' knowledge; the mean knowledge score was 56.6% of the maximum achievable score. There was significant differences in knowledge scores by educational level, employment, income and residence (P = 0.005), (P = 0.008) (P = 0.0122) and (P = 0.009), respectively. Participants had low frequencies of preventive practices, especially females who had a mean total score equivalent to 48.8% of the maximum score, while males' mean score was 54.7% (P = 0.000). Perceived susceptibility was higher among females (83 vs. 74%, P = 0.000), and thus had less perception of the barriers to preventive actions, than men (49.6 vs. 55.5%, P = 0.000). Self-efficacy and perceived benefits had the highest scores (95% of the maximum achievable scores). Considerable number of adult males and females are unaware about osteoporosis. Since there is deficiency in the knowledge, and poor application of the preventive actions. Therefore, Education programs are needed to improve awareness and motivating healthy behaviours.