en Otorhinolaryngology Otorhinolaryngology Original Research Original Research <strong>Background: </strong>Treatment of patients with anosmia is a major therapeutic challenge. The present study evaluated the efficacy of platelet-rich plasma (PRP) in the treatment of anosmia in patients with sinonasal polyposis.<br> <strong>Methods:</strong>In the present clinical trial, atotal of 48 patients with sinonasal polyposis with theIran Smell Identification Test (I-SIT) score of <6 who completed the medical treatment and were observed 3 months after the sinus surgery were included and randomly divided in to 2groups. After endoscopic sinus surgery, the intranasal injection of 1 mL PRP and normal saline was performed in the olfactory region in the intervention and control groups, respectively. Odor function was assessed using the I-SIT at the baseline and at the end of the studyby an independent samples ttest.<br> <strong>Results:</strong> Based on the findings of the present study, the I-SIT improved in both groups during the follow-up, as it reached from 2.63 &plusmn; 2.63 to 5.85 &plusmn; 2.46 after oral steroid administration and 18.93 &plusmn; 1.14 after surgery in the intervention group and from the baseline of 2.10 &plusmn; 2.83 to 5.62 &plusmn; 2.99 after receiving standard medical treatment and 18.43 &plusmn; 1.36in the control groupafter surgery. Although this improvement was significant in both groups in either time interval (all with p<0.001), there was no significant difference between the 2groups in terms of changes in the I-SIT score (p=0.802).<br> <strong>Conclusion:</strong> According to the current study, PRP injection showed no short-term effect on the recovery of olfactory function in patients with sinonasal polyposis. Anosmia, Platelet-Rich Plasma, Olfactory Epithelium, Sinonasal Polyposis 1152 1158 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-6337-1&slc_lang=en&sid=1 Ali Goljanian Tabrizi ali.goljanian@gmail.com 200319475328460091392 200319475328460091392 No Otolaryngology and Head and Neck Surgery Department, Shahid Beheshti University of Medical Sciences, Taleghani Hospital, Tehran, Iran Mahboobe Asadi Ma_asadi@sbmu.ac.ir 200319475328460091393 200319475328460091393 Yes Otolaryngology and Head and Neck Surgery Department, Shahid Beheshti University of Medical Sciences, Taleghani Hospital, Tehran, Iran Mehdi Mohammadi محبوبه اسدی dr.md.mohammadi@gmail.com 200319475328460091394 200319475328460091394 No Otolaryngology and Head and Neck Surgery Department, Shahid Beheshti University of Medical Sciences, Taleghani Hospital, Tehran, Iran Amirhosein Abedi Yekta abedi_yekta@yahoo.com 200319475328460091395 200319475328460091395 No Sport and Exercise Medicine Department, Shahid Beheshti University of Medical Sciences, Taleghani Hospital, Tehran, Iran Mohammadreza Sohrabi m.r.sohrabi@gmail.com 200319475328460091396 200319475328460091396 No Community Medicine Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran