The pharmacokinetic characteristics of a 20-cm² fentanyl 24-hour transdermal patch were compared between 10 healthy elderly subjects 67-87 years and 6 young subjects 19-27 years. All 10 elderly subjects required patch removal prior to 24 h due to adverse effects versus none of the young subjects. The mean patch duration (PD) in elderly subjects was 11.7 ± 4.9 h, yielding a mean area under the curve from 0 to 60 h (AUC_0-60) of 20.4 ± 10.3 ng h/ml versus a mean AUC_0-60 of 21.0 ± 10.4 ng h/ml in young subjects. Correcting AUC_0-60 for PD(AUC_0-60/PD)gave a mean value of 2.05 ± 1.10 ng/ml for elderly subjects, which was significantly greater than the AUC_0-60/PD of 0.88 ± 0.44 ng/ml in young subjects (p = 0.034, Student’s t test). The higher serum concentrations reflect increased absorption and/or decreased clearance in the elderly.