Paruresis, also known as shy bladder syndrome, is a type of phobia in which a person is unable to urinate in the real or imaginary presence of others, such as in a public restroom. The analogous condition that affects bowel movement is called parcopresis or shy bowel.

Some people have brief, isolated episodes of urinary difficulty in situations where other people are in close proximity. Paruresis, however, goes beyond simple shyness, embarrassment, fear of exposure, or fear of being judged for not being able to urinate. Other people may find that they are unable to urinate while in moving vehicles, or are fixated on the sounds of their urination in quiet restrooms or residential settings. In severe cases, a person with paruresis can urinate only when alone at home or through the process of catheterization.

Paruresis is considered a symptom of social anxiety and is correlated with other social anxiety symptoms. When the patient is under the effect of anxiolytics or otherwise disinhibited, paruresis tends to disappear. Paruresis is common among people who underwent a voiding cystourethrography during their childhood.

It appears that paruresis involves a tightening of the sphincter or bladder neck due to a sympathetic nervous system response. The adrenaline rush that produces the involuntary nervous system response probably has peripheral and central nervous system involvement. The internal urethral sphincter (smooth muscle tissue) or the external urethral sphincter (striated muscle), levator ani (especially the pubococcygeus) muscle area, or some combination of the above, may be involved. It is possible that there is an inhibition of the detrusor command through a reflex pathway as well. The pontine micturition center (Barrington's nucleus) also may be involved, as its inhibition results in relaxation of the detrusor and prevents the relaxation of the internal sphincter.

The condition is catered for in the rules for mandatory urine testing for drugs in UK prisons, and, also in the UK, a person with paruresis may be eligible for Universal Credit if their health condition limits their ability to work. It is listed in the NHS approved Healthinote Directory. It is now reported to have been accepted as a valid reason for jury service excusal. From 1 August 2005, the guidance on the rules relating to the testing of those on probation in the UK cites paruresis as a valid reason for inability to produce a sample which is not to be construed as a refusal.

The condition is recognised by the American Urological Association, who include it in their on-line directory of conditions.

Paruresis was described in section 300.23 of the DSM-IV-TR as "performance fears ... using a public restroom" but it was not mentioned by name. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) mentions paruresis by name.

Kaplan & Sadock's Synopsis of Psychiatry states, "Persons with social phobias (also called social anxiety disorder) have excessive fears of humiliation or embarrassment in various social settings, such as in speaking in public, urinating in a public rest room (also called shy bladder), and speaking to a date." The Synopsis describes shy bladder as "inability to void in a public bathroom" and notes that relaxation exercises are an application of behavior therapy for dealing with this disorder. Some paruretics experience delayed urination and must wait for their need to void to overcome their anxiety, while others are unable to urinate at all.