The rising incidence of pertussis amongst adults and adolescents in industrialised countries could be reduced by replacing tetanus and diphtheria (Td) boosters with reduced-antigen-content dT-acellular pertussis (dTpa) vaccines. Repeated administration of a dTpa-IPV (dTpa-inactivated poliomyelitis; Boostrix™ Polio, GlaxoSmithKline) booster to adolescents, 5 years after their previous dose was evaluated. 415 subjects (mean age 11.4 years) who had received either dTpa-IPV or dTpa + IPV at age 4-8 years, all received one dose of dTpa-IPV in this open, phase IV trial. Blood samples were taken before and one-month post-vaccination. Antibody concentrations against D, T, pertussis toxoid (PT), filamentous haemagglutinin (FHA), pertactin (PRN) and polio antigens were determined. Reactogenicity and safety was assessed. Before the second dTpa-IPV booster, the percentage of subjects who were seroprotected/seropositive was: 98.2% (D); 98.5% (T); 40.6% (PT); 99.7% (FHA); 97.0% (PRN); 98.8% (anti-polio 1); 99.7% (anti-polio 2); 97.0% (anti-polio 3). One-month after the second dTpa-IPV dose, all subjects were seroprotected against D, T and polio and anti-pertussis booster responses (seroconversion or ≥2-fold increase) were seen in 93.3% (PT), 93.4% (FHA) and 95.2% (PRN) of subjects. During 4-day follow-up, 4.1% subjects recorded grade 3 pain; 4.6% and 3.6% recorded redness or swelling >50mm, respectively. No serious adverse events were recorded. The incidence of symptoms was not higher than after the previous booster. A second dTpa-IPV booster was highly immunogenic and well tolerated in this population of adolescents, supporting the repeated administration of Boostrix™ Polio. This study is registered at www.clinicaltrials.gov NCT00635128.