Background. All mass gatherings can place travelers at risk for infectious diseases, but the size and density of the annual Hajj pilgrimage to the Kingdom of Saudi Arabia (KSA) present important public health and infection control challenges. This survey of protective practices and respiratory illness among US travelers to the 2009 Hajj was designed to evaluate whether recommended behavioral interventions (hand hygiene, wearing a face mask, cough etiquette, social distancing, and contact avoidance) were effective at mitigating illness among travelers during the 2009 Hajj. Methods. US residents from Minnesota and Michigan completed anonymous surveys prior to and following travel to the 2009 Hajj. Surveys assessed demographics, knowledge, attitudes, and practices (KAP) related to influenza A(H1N1), vaccination, health-seeking behaviors, sources of health information, protective behaviors during the Hajj, and respiratory illness during and immediately after the Hajj. Results. Pre- and post-travel surveys were completed by 186 participants. Respiratory illness was reported by 76 (41.3%) respondents; 144 (77.4%) reported engaging in recommended protective behaviors during the Hajj. Reduced risk of respiratory illness was associated with practicing social distancing, hand hygiene, and contact avoidance. Pilgrims who reported practicing more recommended protective measures during the Hajj reported either less occurrence or shorter duration of respiratory illness. Noticing influenza A(H1N1) health messages during the Hajj was associated with more protective measures and with shorter duration of respiratory illness. Conclusions. Recommended protective behaviors were associated with less respiratory illness among US travelers to the 2009 Hajj. Influenza A(H1N1) communication and education in KSA during the Hajj may also have been an effective component of efforts to mitigate illness. Evaluations of communication efforts and preventive measures are important in developing evidence-based public health plans to prevent and mitigate disease outbreaks at the Hajj and other mass gatherings.