The purpose of this study was to evaluate the bioavailability of diclofenac sodium following stomal or rectal administration in patients after rectal surgery, and to compare it with that following rectal administration in healthy volunteers. Research into the efficacy of different routes of administration of a single dose of a nonsteroidal analgesic suppository (Voltaren®suppository) was carried out in order to investigate the degree of efficacy in patients after rectal surgery, i.e. in patients following rectal amputation (Miles group, n = 5), in patients after sphincter- and anus-preserved colorectal resection (LAR group, n = 5) and in a control group (n = 5). The Miles group demonstrated half the maximum plasma drug concentration (Cmax) and area under the plasma concentration-time curve (AUC) values found in the control group. However, the LAR group showed a plasma concentration curve similar to that of the control group. With regard to absorption of the suppository after rectal surgery, preservation of the proctal canal is a key factor in obtaining normal absorption. In the present study, none of the participating patients complained of discomfort at the application site. As one form of administration for nonsteroidal analgesics, the suppository was found to be effective and useful in patients of both the Miles and LAR groups after rectal surgery in whom oral administration was not possible.