en Otorhinolaryngology Otorhinolaryngology Original Research Original Research <strong>Background: </strong>The occurrence of anosmia/hyposmia during novel Coronavirus disease 2019 (COVID-19) may indicate a relationship between coincidence of olfactory dysfunction and coronavirus disease 2019 (COVID-19). This study aimed to assess the frequency of self-reported anosmia/hyposmia during COVID-19 epidemic in Iran.<br> <strong>&nbsp;&nbsp; Methods: </strong>This population-based cross sectional study was performed through an online questionnaire from March 12 to 17, 2020. Cases from all provinces of Iran voluntarily participated in this study. Patients completed a 33-item patient-reported online questionnaire, including smell and taste dysfunction and their comorbidities, along with their basic characteristics and past medical histories. The inclusion criteria were self-reported anosmia/hyposmia during the past 4 weeks, from the start of COVID-19 epidemic in Iran.<br> <strong>&nbsp;&nbsp; Results: </strong>A total of 10 069 participants aged 32.5&plusmn;8.6 (7-78) years took part in this study, of them 71.13% women and 81.68% nonsmokers completed the online questionnaire. The correlation between the number of olfactory disorders and reported COVID-19 patients in all provinces up to March 17, 2020 was highly significant (Spearman correlation coefficient = 0.87, P< 0.001). A sudden onset of olfactory dysfunction was reported in 76.24% of the participations and persistent anosmia in 60.90% from the start of COVID-19 epidemic. In addition, 80.38% of participants reported concomitant olfactory and gustatory dysfunctions.<br> &nbsp;&nbsp; <strong>Conclusion: An</strong> outbreak of olfactory dysfunction occurred in Iran during the COVID-19 epidemic. The exact mechanisms by which anosmia/hyposmia occurred in patients with COVID-19 call for further investigations.<br> &nbsp; Coronavirus, COVID, COVID-19, SARS-CoV-2, Anosmia, Smell, Hyposmia, Dysgeusia, Taste loss, Gustatory, Olfactory, Olfaction, Infection, ENT 446 452 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-520-1&slc_lang=en&sid=1 Seyed Hamidreza Bagheri 200319475328460064050 200319475328460064050 No ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Alimohamad Asghari asghari.am@iums.ac.ir 200319475328460064051 200319475328460064051 No Skull Base Research Center, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Mohammad Farhadi farhadi28@gmail.com 200319475328460064052 200319475328460064052 No ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Ahmad Reza Shamshiri arshamshiri@tums.ac.ir 200319475328460064053 200319475328460064053 No Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Ali Kabir kabir.a@iums.ac.ir 200319475328460064054 200319475328460064054 No Minimally Invasive Surgery Research Center, Iran University of Medical Sciences, Tehran, Iran Seyed Kamran Kamrava skkamrava@gmail.com 200319475328460064055 200319475328460064055 No ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Maryam Jalessi dr.jalessi@gmail.com 200319475328460064056 200319475328460064056 No Skull Base Research Center, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Alireza Mohebbi mohebbidr@gmail.com 200319475328460064057 200319475328460064057 No ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Rafieh Alizadeh nafiseh.alizadeh@gmail.com 200319475328460064058 200319475328460064058 No ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Ali Asghar Honarmand honarmand@gmail.com 200319475328460064059 200319475328460064059 No Iran Medical Council, Tehran, Iran Babak Ghalehbaghi ghalebaghi.b@iums.ac.ir 200319475328460064060 200319475328460064060 Yes ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran Alireza Salimi arsalimi@sbmu.ac.ir 200319475328460064061 200319475328460064061 No Shahid Beheshti University of Medical Sciences, Tehran, Iran Fatemeh Dehghani Firouzabadi fatemehdehghanifirouzabadi@gmail.com 200319475328460064062 200319475328460064062 No ENT and Head and Neck Research Center and Department, The Five Senses Institute, Iran University of Medical Sciences, Tehran, Iran