Aerococci are only occasionally isolated from urinary tract specimens. A 4-month' survey revealed 29 patients suspected of urinary tract infection (UTI), from whom an Aerococcus-like organism (ALO) was isolated in significant numbers from urinary tract specimens and singly in 11 cases. Approximately 0.8% of all urinary tract specimens examined during the period yielded growth of ALO. The median age of patients was 75 years. Half of the patients were found to have conditions predisposing to UTI. 9 of 11 patients without indwelling catheter, having ALO isolated in pure culture from the urine, showed one or more typical signs of UTI (fever, dysuria and/or pollakisuria and pyuria). A phenotypic comparison was made between 29 strains of ALO and 6 related organisms, including Aerococcus viridans, Streptococcus faecium, Streptococcus sanguis, Streptococcus bovis, Streptococcus Group Q and Streptococcus Group R. ALO and A. viridans showed many similarities, but, owing to characteristic differences with regard to colony morphology, biochemical reactions and antibiotic susceptibility pattern, the strains were easily separated.