Dysthymia (/dɪsˈθaɪmiə/ dihss-THY-mee-ə), known as persistent depressive disorder (PDD) in the DSM-5-TR and dysthymic disorder in ICD-11, is a psychiatric condition marked by symptoms that are similar to those of major depressive disorder, but which persist for at least two years in adults and one year among pediatric populations. The term was introduced by Robert Spitzer in the late 1970s as a replacement for the concept of "depressive personality."

With the DSM-5's publication in 2013, the condition assumed its current name (i.e., PDD), having been called dysthymic disorder in the DSM's previous edition (DSM-IV), and remaining so in ICD-11. PDD is defined by a 2-year history of symptoms of major depression not better explained by another health condition, as well as significant distress or functional impairment.

Individuals with PDD, defined in part by its chronicity, may experience symptoms for years before receiving a diagnosis, if one is received at all. Consequently, they might perceive their dysphoria as a character or personality trait rather than a distinct medical condition and never discuss their symptoms with healthcare providers. PDD subsumed prior DSM editions' diagnoses of chronic major depressive disorder and dysthymic disorder. The change arose from a continuing lack of evidence of a clinically meaningful distinction between chronic major depression and dysthymic disorder.

Dysthymia is characterized by a 2-year history of depressed mood, as well as at least two of the following symptoms: poor appetite or overeating, hypersomnia or insomnia, fatigue or low energy, low self-esteem, poor concentration or difficulty making decisions, and hopelessness. Irritability, rather than sadness, may predominate in the pediatric setting.

Mild degrees of dysthymia may result in withdrawal from stress-inducing activities and avoidance of opportunities for failure. In more severe cases of dysthymia, the patient may withdraw from daily activities. They will usually find little pleasure in usual activities and pastimes, a symptom of depression known as anhedonia.

Diagnosis of dysthymia can be difficult because of the subtle nature of the symptoms and patients can often hide them in social situations, making it challenging for others to detect symptoms. Additionally, dysthymia is often comorbid with other psychological conditions, adding complexity to dysthymia recognition due to overlapping symptoms. Dysthymia is frequently comorbid with anxiety disorders, substance use disorders, and personality disorders, and suicidal ideation is common.

There are no known biological causes that apply consistently to all cases of dysthymia, which suggests diverse origin of the disorder. However, there are some indications that there is a genetic predisposition to dysthymia: "The rate of depression in the families of people with dysthymia is as high as fifty percent for the early-onset form of the disorder." More recent studies have indicated that the frequency of dysthymia is likely influenced more heavily by "family environmental and non-shared environmental factors," rather than genetic or neurobiological factors. Part of the reason for the uncertainty with regard to understanding the biological basis of dysthymia is due to the lack of genetic and neurobiological research, genome wide studies, and "grossly underpowered sample sizes." Other factors linked with dysthymia include stress, social isolation, and lack of social support.

In a 1998 study using identical and fraternal twins, results indicated that there was not a stronger likelihood of identical twins both having dysthymia than fraternal twins. This provides support for the idea that dysthymia does not have a consistent genetic basis.