During the last few years, prostate cancer is more frequently diagnosed in young patients. This lays emphasis on the necessity to preoperatively evaluate the sexual function in patients undergoing bilateral nerve sparing radical retropubic prostatectomy (BNSRRP). The aim of our study was to make an objective evaluation of the basic sexual function in patients with clinically localized prostate cancer and candidates for BNSRRP, using internationally validated questionnaires. We also tried to find a correlation between these questionnaires and the individual assessment of candidates, on one hand, and between comorbidities of the patients and degree of erectile dysfunction (ED), on the other hand. From January 2014 to March 2017, at the urology clinic of University Hospital – Pleven, 64 patients opted BNSRRP and reported to have preserved erectile function (EF), wishing to maintain this function after surgery. The patients’ histories and comorbidities were recorded on the day of hospitalization. The subjective assessment of the patients’ potency was compared with International Index of Erectile Function (IIEF). According to the EF domain of the IIEF, baseline EF was assessed in 28 patients. Twelve patients had mild ED, 9 patients had mild to moderate ED, seven patients had moderate, and eight had severe ED. The results showed that a significant number of patients with clinically localized prostate cancer who were candidates for BNSRRP reported to be fully potent but actually had impaired EF preoperatively. There was also a pronounced correlation between concomitant diseases and EF.