Bladder outlet obstruction (BOO) in women is thought to be present in between 2.7% and 27%. Causes of BOO in women may be anatomical or functional. Yet, unlike the diagnosis in men, there is no standard definition for BOO in women, and no universally accepted diagnostic criteria. This interesting paper from London reports the development of a nomogram for classifying BOO derived from concurrent peak flow rate (Qmax), corresponding voiding pressure (Pdet.Qmax) and radiographic evidence of obstruction on videourodynamics (VCMG). Based on a retrospective review of VCMG and clinical data including the underlying cause of obstruction, data from 647 women were divided into seven groups. Cluster analysis was used to identify the axis that best separates the radiographically obstructed and unobstructed as PdetQmax = 2*Qmax. Alternatively, a female BOO index (BOOIf) may be calculated mathematically by using the formula BOOIf = PdetQmax – 2.2*Qmax. BOOIf >18% correlates with >90% certainty of obstruction, BOOIf >5 has a 50% likelihood of obstruction and BOOIf <0 has a less than 10% probability of obstruction. There are several nomograms in existence for use in women, but this one is unique in its incorporation of VCMG criteria for defining obstruction. However, in clinical practice it is not essential to have a VCMG available to diagnose BOO in women.