AIM: To present the frequency of intraoperative floppy iris syndrome (IFIS) in cataract patients who taking alpha 1-a receptor antagonist (ARA) drugs, and evaluate the predictive value of pupil diameter (PD) changes in IFIS patients. METHODS: Male cataract patients who are under treatment with alpha-1a-ARAs (alfuzosin, tamsulosin) intraoperatively were evaluated and were grouped as with/without IFIS. The preoperative PD values were compared with controls. Also, the intraoperative manipulations and early/late complications were recorded. RESULTS: A total of 77 patients (77 eyes) of 94 benign prostate hyperplasia (BPH) patients have been defined as IFIS (81.91%) and 40 patients (40 eyes) were taking tamsulosin and 37 patients (37 eyes) were taking alfuzosin. During the cataract surgery, the rate of posterior capsular rupture (P=0.754), vitreous loss (P=0.585), iris tears (P=0.004), and iris catching (P=0.000) were higher in IFIS group, but the difference was significant only in the iris catching. At the postoperative first-month visit, persistent IOP rise and iris stromal tears were more frequent in IFIS group, but the difference was not significant (P=0.311, P=0.146; respectively). In contrast, Descemet membrane detachment was insignificantly more frequent in controls (P=0.311). In IFIS and control patients, PDs were 9.54±1.78 and 9.72±1.57 mm (P=0.255) under scotopic illumination, 8.54±1.43 and 8.74±1.25 mm (P=0.289) under mesopic illumination, 6.99±1.35 and 7.27±1.39 mm (P=0.662) under photopic illumination, respectively. However PDs were lower in IFIS under all illumination degrees, no significant difference was detected between groups. CONCLUSION: IFIS is a significant clinical syndrome with an increased intraoperative/postoperative complication ratio. The prediction of this syndrome is important because of prevention required precautions against possible complications. There is no association between IFIS and preoperative PD.