Background: Treatment of adolescents who stutter is an under-researched area that would benefit from greater attention. Aims: To investigate whether an intensive treatment programme for older teenagers who stutter, aged over 16 years of age, is effective in reducing overt and covert aspects of stuttering. Methods & Procedures: A repeated-measures, single-subject experimental design was replicated across participants. The study consisted of a 5-week baseline phase, 2-week intensive treatment phase, 5-week consolidation phase and 10-month follow-up phase. Participants were asked to make ten video recordings at home during each phase, while completing a reading and a conversation task. Recordings were analysed in terms of the percentage of stuttered syllables using a simplified time-series analysis. Participants completed self-report questionnaires at predetermined times throughout the study. Data are presented for three males aged 17;7, 17;11 and 18;10. Outcomes & Results: One participant completed all required recordings. Difficulties were encountered collecting follow-up data with the other two participants and data are available up to 5 months after the intensive therapy phase. A significant trend of reduced frequency of stuttering was found for all three participants during the intensive therapy phase. This trend continued throughout the consolidation phase and remained significant when available longer-term data were included in the analysis. Participants also reported increased self-efficacy about speaking and reduced overt and covert aspects of stammering. Conclusions & Implications: Findings show that this therapy programme for teenagers had a significant treatment effect for the participants studied in the short- and medium-term, however longer-term data were not available for all participants. Issues in conducting research with this client group are discussed.