Objective The effect of antibiotics on survival in patients with pulmonary Pseudomonas aeruginosa is controversial. The aim of this study is to i) determine the prevalence of adequate antibiotic treatment of P. aeruginosa in an unselected group of adult non-cystic fibrosis patients and ii) to assess the overall mortality in study patients treated with adequate vs. non-adequate antibiotics. Methods Prospective, observational study of all adult patients with culture verified P. aeruginosa from 1 January 2010-31 December 2012 in Region Zealand, Denmark. Patients with cystic fibrosis were excluded. Adequate therapy was defined as any antibiotic treatment including at least one antipseudomonal beta-lactam for a duration of at least 10 days. Furthermore, P. aeruginosa had to be tested susceptible to the given antipseudomonal drug and treatment had to be approved by senior clinician to fulfil the adequate-criteria. Results A total of 250 patients were identified with pulmonary P. aeruginosa. The vast majority (80%) were treated with non-adequate antibiotic therapy. All-cause mortality rate after 12 months was 49% in adequate treatment group vs. 52% in non-adequate treatment group. Cox regression analysis adjusted for age, gender, bacteraemia, comorbidities and bronchiectasis showed no significant difference in mortality between treatment groups (adequate vs. non-adequate: hazard ratio 0.95, 95% CI 0.59-1.52, P = 0.82). Conclusion Adequate antipseudomonal therapy was only provided in a minority of patients with pulmonary P. aeruginosa. Adequate therapy did not independently predict a favourable outcome. New research initiatives are needed to improve the prognosis of this vulnerable group of patients.