Objective: Determine how serum prostate-specific antigen (t-PSA) levels and free PSA (f/t PSA) ratio change following transurethral resection of the prostate (TURP). Results: Clinical improvement after TURP, reflected by I-PSS score, was demonstrated as early as 30 days and remained stable until the end of the follow-up. Mean t-PSA declined 71% after TURP and 60 days after surgery the reduction reached its peak, stabilizing afterwards. It varied from 6.19 ± 7.06 ng/mL before surgery to 1.75 ± 1.66 ng/mL on day 60 (p < 0.001). The mean baseline f/t PSA ratio was 18.2% ± 3.4% and was not significantly changed at any given time point in the postoperative period (p = 0.91). There were also no statistically significant differences in t-PSA or f/t PSA between patients with and without prostatitis at any time point (p = 0.23). Resected prostate fragments weighed 29.9 ± 19.6 g, corresponding to 39.1% of the estimated preoperative prostate volume. Each gram of tissue resected decreased PSA by 0.15 ± 0.11 ng/mL, while 1% prostate volume resected led to a reduction of 2.4% ± 0.4% in serum PSA from baseline. Conclusions: PSA decreases drastically in patients who undergo TURP. These low levels stabilize within 60 days after surgery. The f/t PSA ratio did not change, and the finding of chronic prostatitis did not affect the levels of these variables.