Encopresis (from Ancient Greek ἐγκόπρησις, enkóprēsis) is voluntary or involuntary passage of feces outside of toilet-trained contexts (fecal soiling) in children who are four years or older and after an organic cause has been excluded. Children with encopresis often leak stool into their undergarments.

This term is usually applied to children, and where the symptom is present in adults, it is more commonly known as fecal incontinence (including fecal soiling, fecal leakage or fecal seepage).

(In)voluntary soiling of undergarments. There are two types: with or without constipation. Those with constipation may experience decreased appetite, abdominal pain, have pain on defecation, have fewer bowel movements, and have hard or soft stools. Those without constipation do not have these symptoms.

Encopresis is commonly caused by constipation in children, by reflexive withholding of stool, by various physiological, psychological, or neurological disorders, or from surgery (a somewhat rare occurrence).

The colon normally removes excess water from feces. If the feces or stool remains in the colon too long due to conditioned withholding or incidental constipation, so much water is removed that the stool becomes hard, and becomes painful for the child to expel in an ordinary bowel movement. A vicious cycle can develop, where the child may avoid moving his/her bowels in order to avoid the "expected" painful toilet episode. This cycle can result in so deeply conditioning the holding response that the rectal anal inhibitory response (RAIR) or anismus results. The RAIR has been shown to occur even under anesthesia and when voluntary control is lost. The hardened stool continues to build up and stretches the colon or rectum to the point where the normal sensations associated with impending bowel movements do not occur. Eventually, softer stool leaks around the blockage and cannot be withheld by the anus, resulting in soiling. The child typically has no control over these leakage accidents, and may not be able to feel that they have occurred or are about to occur due to the loss of sensation in the rectum and the RAIR. Strong emotional reactions typically result from failed and repeated attempts to control this highly aversive bodily product. These reactions then in turn may complicate conventional treatments using stool softeners, sitting demands, and behavioral strategies.

The onset of encopresis is most often benign. The usual onset is associated with toilet training, demands that the child sit for long periods of time, and intense negative parental reactions to feces. Beginning school or preschool is another major environmental trigger with shared bathrooms. Feuding parents, siblings, moving, and divorce can also inhibit toileting behaviors and promote constipation. An initiating cause may become less relevant as chronic stimuli predominate.

The psychiatric (DSM-5) diagnostic criteria for encopresis are:

The DSM-5 recognizes two subtypes: with constipation and overflow incontinence, and without constipation and overflow incontinence. In the subtype with constipation, the feces are usually poorly formed and leakage is continuous, and this occurs both during sleep and waking hours. In the type without constipation, the feces are usually well-formed, soiling is intermittent, and feces are usually deposited in a prominent location. This form may be associated with oppositional defiant disorder (ODD) or conduct disorder, or may be the consequence of large anal insertions, or more likely due to chronic encopresis that has radically desensitized the colon and anus.