Our objective was to determine the incidence of inguinal hernia (IH) after surgery for prostatic diseases. Medical records of 395 patients who underwent radical retropubic prostatectomy (RRP; n = 155), open simple prostatectomy (OP; n = 35), or transurethral resection of the prostate (TURP; n = 205) at the Chibaken Saiseikai Narashino Hospital from April 2000 to March 2007 were retrospectively evaluated. The incidence of IH was 23.9% in the RRP group, 18.9% in the OP group, and 2% in the TURP group. Overall, 91.9% in the RRP and 83.3% in the OP group developed an IH within 2 years postoperatively. The laterality of IH after open surgery was mainly on the right side. Subclinical IH were seen in 25% of RRP cases. The existence of subclinical IH was the only significant risk factor for postoperative IH in this analysis. Furthermore, OP and RRP procedures significantly increased the risk of postoperative IH compared with TURP. The hernia-free ratios were significantly lower after RRP and OP than after TURP (vs RRP: P < 0.001; vs OP: P < 0.001). Our findings confirm that a lower abdominal incision itself is associated with postoperative IH in patients undergoing prostate surgery. Attention must be paid to pre-existing subclinical IH through careful preoperative assessment. Patients should be followed for more than 2 years due to the high incidence of postoperative IH.