This study compares the incidence, degree, and length of postoperative pain in 300 endodontically treated teeth, with and without apical patency, in relation to some diagnostic factors (vitality, presence of preoperative pain, group, and mandible of treated tooth). Of the questionnaires received back, apical patency was maintained during shaping procedures with a #10 K-file in one group (n = 115) and not in the other (n = 121). There was significantly less postendodontic pain when apical patency was maintained in nonvital teeth. If pain appeared, its duration was longer when apical patency was maintained in teeth with previous pain or located in the mandible. Maintenance of apical patency does not increase the incidence, degree, or duration of postoperative pain when considering all variables together.