BACKGROUND: In 2012, Fiji became the first independent Pacific island country to introduce rotavirus vaccine. We describe the impact of rotavirus vaccine on all-cause diarrhoea admissions in all ages, and rotavirus diarrhoea in children <5 years of age. METHODS: An observational study was conducted retrospectively on all admissions to the public tertiary hospitals in Fiji (2007-2018) and prospectively on all rotavirus-positive diarrhoea admissions in children <5 years at two hospital sites (2006-2018, and 2010-2015), along with rotavirus diarrhoea outpatient presentations at one secondary public hospital (2010-2015). The impact of rotavirus vaccine was determined using incidence rate ratios (IRR) of all-cause diarrhoea admissions and rotavirus diarrhoea, comparing the pre-vaccine and post-vaccine periods. All-cause admissions were used as a control. Multiple imputation was used to impute missing stool samples. FINDINGS: All-cause diarrhoea admissions declined among all age groups except among infants ≤2 months old and adults ≥55 years. For children <5 years, all-cause diarrhoea admissions declined by 39% (IRR)=0•61, 95%CI; 0•57-0•65, p-value<0•001). There was an 81% (95%CI; 51-94%) reduction in mortality among all-cause diarrhoea admissions in children under <5 years. Rotavirus diarrhoea admissions at the largest hospital among children <5 years declined by 87% (IRR=0•13, 95%CI; 0•10-0•17, p-value<0•001). Among rotavirus diarrhoea outpatient presentations, the IRR was 0•39 (95%CI; 0•11, 1.21, p-value=0.077). INTERPRETATIONS: Morbidity and mortality due to rotavirus and all-cause diarrhoea in Fiji has declined in people aged 2 months to 54 years after the introduction of the RV vaccine. FUNDING: Supported by WHO and the Australian Government.