Postoperative residual paralysis is an important complication of the use of neuromuscular blocking drugs. In this prospective study, the incidence of residual paralysis detected as a train-of-four response <90% was less frequent in surgical outpatients (38%) than inpatients (47%) (P = 0.001). This might have been the result of the more frequent use of mivacurium for outpatients. Before undertaking tracheal extubation, the anesthesiologists had applied clinical criteria (outpatients, 49%; inpatients, 45%), pharmacological reversal (26%, 25%), neuromuscular transmission monitoring (12%, 11%), or a combination of these. None of these measures seemed to reduce the incidence of residual paralysis except for quantitative train-of-four monitoring. Postoperatively, eight individual clinical tests or a sum of these tests were also unable to predict residual paralysis by train-of-four. Although the incidence of residual paralysis was less frequent in surgical outpatients, predictive criteria were not evident.