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Background Non-tuberculous mycobacteria (NTM) have emerged as significant pathogens in non-cystic fibrosis (CF) bronchiectasis. While Mycobacterium avium and M. intracellulare are considered the dominant MAC species across Europe and North America, our UK-based cohort revealed a striking shift toward M. chimaera predominance. In addition, we observed an under-recognised burden of nutritional risk and NTM disease in patients without underlying lung conditions.Methods We retrospectively reviewed all non-CF patients treated for NTM infection at a UK tertiary centre between January 2020 and December 2024. Data on demographics, NTM species, disease classification, BMI, comorbidities, immunosuppression, and lifestyle factors were collected and compared to published European and global cohort data.Results Among 48 patients (67% male, mean age 66.3), M. chimaera was the leading species, accounting for 71% of isolates far exceeding the 10–20% typically reported in European MAC cohorts. Other species included M. avium (8%), M. marinum (6%), and several less commonly reported species such as M. porcinum, M. fortuitum, and M. malmoense.COPD (44%) and bronchiectasis (23%) were the most common comorbidities, but notably, 17% of patients (n=8) had no underlying lung disease. Within this subgroup, 5 had extrapulmonary NTM (NTM-EP), 2 had pulmonary involvement (NTM-PD), and 1 had disseminated infection. Species in this group were diverse and included M. chimaera (2), M. marinum (2), M. avium, M. porcinum, M. malmoense, and M. fortuitum. Three were immunosuppressed and three had a BMI ≤21 highlighting the vulnerability of non-traditional hosts.Nutritional risk was a common theme throughout the cohort. The mean BMI was 21.3 (range 11–32), and 33% of patients had a BMI below 20. Smoking (73%) and alcohol use (17%) were also prevalent. Most patients (85%) had NTM-PD, while 13% had NTM-EP, and 2% had disseminated infection. HIV prevalence was low (4%).Conclusions This cohort highlights an evolving epidemiological trend in the UK, with M. chimaera emerging as the predominant MAC subspecies challenging current assumptions based on continental European data. Routine species-level identification, integrating nutritional assessments, and multi-disciplinary care could improve diagnostic precision and clinical outcomes in this growing patient group.