A prospective cohort study was conducted to estimate the incidence of acute respiratory infections (ARI) among hajjis registered at primary health care centres of Riyadh. Out of 1027 hajjis, 39.8% developed symptoms of ARI. The incidence of ARI was not statistically significantly associated with age, sex, educational status or smoking. The risk of illness was significantly higher among diabetics, hajjis who stayed longer in the hajj area and who prayed at Namera mosque. Use of a facemask by men, but not use of a facecover by women, was a significant protective factor against ARI.