Right pneumothorax complicated by an endocardial atrial lead has never been reported. Herein, we report on a small-build 79-year-old Taiwanese woman who suffered from complete AV block and underwent dual-chamber permanent pacemaker implantation. An active fixation screw-in atrial lead was chosen. The procedure was complicated by right pneumothorax associated with atrial perforation. Since simple measurements of the implantation parameters could not be used to predict the occurrence of perforation, great caution should be taken in to avoid overscrewing the atrial lead, and in scrutinizing the penetration depth of the helix of the lead under fluoroscopy.