Retention of functionless pacemaker leads may occur following mechanical or infective problems (potentially or definitely infected) or after electrical failure of the lead. One hundred nineteen patients with a pacemaker lead (or leads) retained between 1970 and 1990 were reviewed retrospectively. Lead retention after an intervention dictated by potential or definite infection of the pacing system resulted in complications in 27 of 53 patients (51%), which in 22 patients (42%) were major (septicemia, superior vena cava syndrome, and further surgery under general anesthesia for recurrent "infective" problems) including three deaths. Complications were less likely if lead retention occurred after electrical failure with three minor and two major (surgery under general anesthesia, superior vena cava syndrome) complications in 66 patients (P less than 0.001). Bacteriology of swabs taken at the time of retention in the patients with potential or definite infection was unhelpful in predicting future complications: 8/18 patients (44%) whose swabs were negative had complications of which 5/18 (28%) were major. In our experience retention of functionless pacemaker leads after an intervention dictated by potential or definite infection of the pacing system, is associated with significant morbidity and mortality and should be avoided.