BACKGROUND: This study assessed if bronchiectasis (BR) and rheumatoid arthritis (RA), when manifesting as an overlap syndrome (BROS), were associated with worse outcomes than other BR etiologies applying the Bronchiectasis Severity Index (BSI). METHODS: Data were collected from the BSI databases of 1,716 adult patients with BR across six centers: Edinburgh, United Kingdom (608 patients); Dundee, United Kingdom (n = 286); Leuven, Belgium (n = 253); Monza, Italy (n = 201); Galway, Ireland (n = 242); and Newcastle, United Kingdom (n = 126). Patients were categorized as having BROS (those with RA and BR without interstitial lung disease), idiopathic BR, bronchiectasis-COPD overlap syndrome (BCOS), and "other" BR etiologies. Mortality rates, hospitalization, and exacerbation frequency were recorded. RESULTS: A total of 147 patients with BROS (8.5% of the cohort) were identified. There was a statistically significant relationship between BROS and mortality, although this relationship was not associated with higher rates of BR exacerbations or BR-related hospitalizations. The mortality rate over a mean of 48 months was 9.3% for idiopathic BR, 8.6% in patients with other causes of BR, 18% for RA, and 28.5% for BCOS. Mortality was statistically higher in patients with BROS and BCOS compared with those with all other etiologies. The BSI scores were statistically but not clinically significantly higher in those with BROS compared with those with idiopathic BR (BSI mean, 7.7 vs 7.1, respectively; P < .05). Patients with BCOS had significantly higher BSI scores (mean, 10.4), Pseudomonas aeruginosa colonization rates (24%), and previous hospitalization rates (58%). CONCLUSIONS: Both the BROS and BCOS groups have an excess of mortality. The mechanisms for this finding may be complex, but these data emphasize that these subgroups require additional study to understand this excess mortality.