Overactive bladder (OAB) is a diagnosis resulting from a combination of multiple underlying factors. Current traditional treatments are based on anticholinergic blockade which have marginal benefits and are associated with poor tolerability and continuation rates. There is mounting evidence that chronic low grade bacterial bladder colonisation may exacerbate OAB symptoms and may explain why the current treatment strategies are not always successful. However, standard diagnostic laboratory tests to identify the presence of such bacterial infection are unreliable. Newer technologies such as RNA sequencing and extended culture techniques, show that urine is not sterile and organisms that are found in urine may be responsible for OAB symptoms. This article aims to review the current evidence suggesting that micro-organisms in urine may be important in the aetiology of OAB or may exacerbate OAB symptoms.