The overactive bladder (OAB) is a well-known and common urologic condition. However, the apparent opposite syndrome to the OAB, the underactive bladder (UAB), remains an enigma. Underactive bladder syndrome is complex condition that shares symptoms with other prevalent urologic diagnoses. UAB is not a pure condition-it is not the result of any single factor, but rather, it is multifactorial. As a result, UAB may overlap with OAB, bladder outlet obstruction, or even occur with no symptoms or associated diseases. To make it yet more challenging, in the elderly, detrusor hyperreflexia/impaired contractility (DHIC) is a condition that has the pathological elements of both OAB and UAB and is also common. I hypothesize that UAB and OAB may not be an entirely separate disease entity. Instead, chronic untreated or treatment refractory OAB--due to neurological diseases such as diabetes, bladder outlet obstruction or aging sarcopenia and frailty--may progress to DHIC and, finally, UAB. The progression of OAB to UAB hypothesis suggests that early education, behavioral modification and medical treatment may alter and/or prevent progression to UAB.