Introduction. P. aeruginosa is an opportunistic Gram-negative pathogen frequently isolated in urinary tract infections (UTI) affecting elderly and catheterized patients and associated with ineffective antibiotic treatment and poor clinical outcomes. Gap statement. Invasion has been shown to play an important role in UTI caused by E. coli but has only recently been studied with P. aeruginosa . The ability of P. aeruginosa to adapt and evolve in chronic lung infections is associated with resistance to antibiotics but has rarely been studied in P. aeruginosa UTI populations. Aim. We sought to determine whether phenotypic and genotypic heterogeneity exists in P. aeruginosa UTI isolates and whether, like urinary pathogenic Escherichia coli , these could invade human bladder epithelial cells – two factors that could complicate antibiotic treatment. Methodology. P. aeruginosa UTI samples were obtained from five elderly patients at the Royal Liverpool University Hospital as part of routine diagnostics. Fourty isolates from each patient sample were screened for a range of phenotypes. The most phenotypically diverse isolates were genome sequenced. Gentamicin protection assays and confocal microscopy were used to determine capacity to invade bladder epithelial cells. Results. Despite significant within-patient phenotypic differences, no UTI patient was colonized by distinct strains of P. aeruginosa . Limited genotypic differences were identified in the form of non-synonymous SNPs. Gentamicin protection assays and confocal microscopy provided evidence of P. aeruginosa ’s ability to invade bladder epithelial cells. Conclusions. Phenotypic variation and cell invasion could further complicate antibiotic treatment in some patients. More work is needed to better understand P. aeruginosa UTI pathogenesis and develop more effective treatment strategies.