BACKGROUND: Most antibiotic prescribing for upper respiratory tract infections (URTIs) and acute bronchitis is inappropriate. Substantive and sustained reductions in prescribing are needed to reduce antibiotic resistance. Prescribing habits develop early in clinicians' careers. Hence, general practice (GP) trainees are an important group to target. OBJECTIVES: We aimed to establish temporal trends in antibiotic prescribing for URTIs and acute bronchitis/bronchiolitis by Australian GP trainees (registrars). METHODS: A longitudinal analysis, 2010-2019, of the Registrars Clinical Encounters in Training (ReCEnT) dataset. In ReCEnT, registrars record clinical and educational content of 60 consecutive consultations, on 3 occasions, 6 monthly. Analyses were of new diagnoses of URTI and acute bronchitis/bronchiolitis, with the outcome variable a systemic antibiotic being prescribed. The independent variable of interest was year of prescribing (modelled as a continuous variable). RESULTS: 28,372 diagnoses of URTI and 5,289 diagnoses of acute bronchitis/bronchiolitis were recorded by 2,839 registrars. Antibiotic prescribing for URTI decreased from 24% in 2010 to 12% in 2019. Prescribing for acute bronchitis/bronchiolitis decreased from 84% to 72%. "Year" was significantly, negatively associated with antibiotic prescribing for both URTI (odds ratio [OR] 0.90; 95% confidence interval [CI]: 0.88-0.93) and acute bronchitis/bronchiolitis (OR 0.92; 95% CI: 0.88-0.96) on multivariable analysis, with estimates representing the mean annual change. CONCLUSIONS: GP registrars' prescribing for URTI and acute bronchitis/bronchiolitis declined over the 10-year period. Prescribing for acute bronchitis/bronchiolitis, however, remains higher than recommended benchmarks. Continued education and programme-level antibiotic stewardship interventions are required to further reduce registrars' antibiotic prescribing for acute bronchitis/bronchiolitis to appropriate levels.