Abstract: Background Although the burden of bronchiectasis is globally recognised, there is limited paediatric data particularly on trends over the years. There is also no published data on whether vitamin D deficiency/insufficiency and human T-cell lymphotropic virus type 1 (HTLV-1) infection, both found to relate with severe bronchiectasis in First Nations adults, is also important in children with bronchiectasis. Research Question Among children with bronchiectasis, has (a) the clinical and bronchoalveolar lavage (BAL) profiles changed between two 5-year periods (period-1=2007-11, period-2=2012-16); and (b) is vitamin D deficiency/insufficiency and/or HTLV-1 infection associated with radiological severity of bronchiectasis? Study Design and Methods We analysed the data from children with bronchiectasis prospectively enrolled at Royal Darwin Hospital, Australia at their first diagnosis i.e. no child was in both time-periods. Data collected include demographics, BAL, bloods and computed tomography chest scan evaluated using the Bhalla and modified Bhalla scores. Results The median age of the 299 children was 2.2 years (interquartile range 1.5-3.7), 168 (56%) males and most were First Nations (92%). Overall, bronchiectasis was high over time, particularly among First Nations children. In the later period, numbers of non-First Nations more than tripled, but did not reach statistical significance. In period-2 compared to period-1, fewer First Nations children had chronic cough (period-1=61%, period-2=47%, p=0.03), were younger, less likely to have received azithromycin (period-1=42%, period-2=21%, p<0.001) and their BAL had lower Haemophilus influenzae and Moraxella catarrhalis infection. HTLV-1 was not detected and vitamin D deficiency/insufficiency did not correlate with severity of bronchiectasis. Interpretation Bronchiectasis remains high particularly among First Nations children. Important changes that arguably reflect improvements were present, but overall, profiles remained similar. Although Vitamin D deficiency was uncommon, its role in children with bronchiectasis requires further evaluation. HTLV-1 was non-existent and is unlikely to play any role in First Nations children with bronchiectasis.