BACKGROUND: In Ulaanbaatar, the first case of the pandemic influenza infection has been reported on 12 October 2010.By November 9, a total of 929 cases laboratory-confirmed had been reported to National Center for CommunicableDiseases (NCCD). Of these cases reported, 9 people died.METHODS: The objectives of the study were to describe patients who admitted and hospitalized at NCCD and to determineoverall attack rates among health workers, secondary attack rates among students of colleges and universities. Datawas analyzed using Epi-Info2000.RESULTS: Among 929 of laboratory-confirmed cases, 50.3% (95% CI 43.0-57.5) were males aged 23 (±14.9) in averagewith youngest – 7 months, oldest – 76 years old. Data analysis by districts among the hospitalized patients, showed32.8% (139) of total cases in Bayanzurkh district including the first case of the pandemic influenza infection. The majorityof patients who admitted and hospitalized to NCCD mostly experienced fever (288, 68.1%), dry cough (251, 59.3%),headache (203, 48.0%), sore throat (175, 41.6%). With 1020 physicians and health workers in total, 41.4% (422) ofthem work at NCCD, 35.4% (361) – at MCHRC. 11.1% of health workers out of total become ill with pandemic H1N12009 (overall attack rate 11.1%) with the most common symptom, 380C and higher fever (100.0%, 113), sore throat(83.2%, 94), cough (76.1%, 86) and runny nose (59.3%, 67). The higher attack rates of health workers by occupationwere doctor (18.0%) and auxiliary (13%). The secondary attack rates among university students for influenza-likeillness(ILI) were 12.9%. These secondary attack rates were higher among students of art’s college as compared withother universities (52.4%). For students, the main clinical symptoms were fever + sore throat (75.0%, 18), fever+ cough(70.8%, 17).DISCUSSION: In China, as of 27 September, 2009, from reported total 19981 cases infected with pandemic influenza,61.0% were males, mean age was 17, mainly affected with 83% school students that consistent with our study result.The similar results on clinical symptoms were obtained in Russia. Out of 130 patients, 28.6% had 380Ñ and higherfever, for 54.3% the body temperature reached 38.1-390Ñ where as 17.1% - higher 390Ñ and 96% had cough, 89%had muscle ache, 65% had headache, 14% had diarrhea.