OBJECTIVE To evaluate the impact of a peer-referral and clinic welcome programme for reducing barriers to adolescents' uptake of family planning services in Uganda. METHODS We developed an intervention using behavioural design and carried out a stratified, randomized controlled evaluation of the intervention in girls aged 15-19 years. Sexual and reproductive health clinics were randomized into control (56 clinics) and intervention groups (60 clinics). All intervention clinics received the core intervention (materials to create an adolescent-friendly environment and referral cards to give to friends), while a subset of clinics additionally received training in youth-friendly service provision. We collected clinics' routine data on monthly numbers of visits by adults and adolescents over a 15-month baseline and 6-month intervention period, 2018-2020. RESULTS In multivariate regression analysis we found significant effects of the intervention on primary outcomes in the pooled intervention group compared with control. Mean monthly visits by adolescents increased by 45% (incidence rate ratio, IRR: 1.45; 95% confidence interval, CI: 1.14-1.85), or over five additional adolescent clients per clinic per month. The mean adolescent proportion of total clients improved by 5.3 percentage points (95% CI: 0.02-0.09). Within treatment arms, clinics receiving the training in youth-friendly service provision showed the strongest effects: a 62% increase (IRR: 1.62; 95% CI: 1.21-2.17) in adolescent clients, or over seven additional adolescents per clinic per month, relative to the control group. CONCLUSIONS A behavioural change intervention designed to target identified barriers can increase adolescents' uptake of family planning counselling and services.