Since the description of the overactive bladder (OAB) syndrome, which excludes infection, the precise definition of significant bacteriuria in these women is critical. The traditional definition of ‘significant’ bacteriuria is >105 colony-forming units/ml which was described 50 years ago by a renal physician whose primary interest was the prevention of pyelonephritis. Subsequent studies have shown this to be an insensitive threshold in women with acute lower urinary tract symptoms. Bacterial counts between 102 and 105 CFU/ml (‘low-count bacteriuria’) are now considered important in women with acute dysuria and warrant treatment. However, these findings have been slow to translate into routine clinical practice. In addition, the role of low-count bacteriuria in women with OAB symptoms (frequency/urgency/nocturia) without dysuria is poorly studied. One recent study has shown low-count bacteriuria to be more prevalent among women with severe OAB than bacteriuria >105 CFU/ml. We present an outline of the history of this issue and summarise current microbiological and clinical concepts. Neurourol. Urodynam. 30:32–37, 2011. © 2010 Wiley-Liss, Inc.