The DSM-IV-TR defines this disorder, "Hypochondriasis," as a somatoform disorder and one study has shown it to affect about 3% of the visitors to primary care settings.

Hypochondria is often characterized by fears that minor bodily symptoms may indicate a serious illness, constant self-examination and self-diagnosis, and a preoccupation with one's body. Many individuals with hypochondriasis express doubt and disbelief in the doctors' diagnosis, and report that doctors’ reassurance about an absence of a serious medical condition is unconvincing, or un-lasting. Many hypochondriacs require constant reassurance, either from doctors, family, or friends, and the disorder can become a disabling torment for the individual with hypochondriasis, as well as his or her family and friends. Some hypochondriacal individuals completely avoid any reminder of illness, whereas others frequently visit doctors’ offices. Other hypochondriacs will never speak about their terror, convinced that their fear of having a serious illness will not be taken seriously by those in whom they confide.

Hypochondriasis manifests in various ways. Some people have numerous intrusive thoughts and physical sensations that push them to check with family, friends and physicians. Other people are so afraid of any reminder of illness that they will avoid medical professionals for a seemingly minor problem, sometimes to the point of becoming neglectful of their health when a serious condition may exist and go undiagnosed. Again, some people are afraid of getting a disease because they have a disease. Yet, some others live in despair and depression, certain that they have a life-threatening disease and no physician can help them. Some consider the disease as a punishment for past misdeeds.

Hypochondriasis is often accompanied by other psychological disorders. Clinical depression, obsessive-compulsive disorder (also known as OCD), phobias and somatization disorder are the most common accompanying conditions in people with hypochondriasis, as well as a generalized anxiety disorder diagnosis at some point in their life.

Many people with hypochondriasis experience a cycle of intrusive thoughts followed by compulsive checking, which is very similar to the symptoms of obsessive-compulsive disorder. However, while people with hypochondriasis are afraid of having an illness, patients with OCD worry about getting an illness or of transmitting an illness to others. Although some people might have both, these are distinct conditions.

Patients with hypochondriasis often are not aware that depression and anxiety produce their own physical symptoms that might be mistaken for signs of a serious medical disease. For example, people with depression often experience changes in appetite and weight fluctuation, fatigue, decreased interest in sex and motivation in life overall. Intense anxiety is associated with rapid heart beat, palpitations, sweating, muscle tension, stomach discomfort, and numbness or tingling in certain parts of the body (hands, forehead, etc.).[citation needed]

Cyberchondria is a colloquial term for hypochondria in individuals who have researched medical conditions on the Internet. The media and the Internet often contribute to hypochondria, as articles, TV shows and advertisements regarding serious illnesses such as cancer and multiple sclerosis (some of the diseases hypochondriacs commonly think they have) often portray these diseases as being random, obscure and somewhat inevitable. Inaccurate portrayal of risk and the identification of non-specific symptoms as signs of serious illness contribute to exacerbating the hypochondriac’s fear that they actually have that illness.

Major disease outbreaks or predicted pandemics can also contribute to hypochondria. Statistics regarding certain illnesses, such as cancer, will give hypochondriacs the illusion that they are more likely to develop the disease. A simple suggestion of mental illness can often trigger one with hypochondria to obsess over the possibility.

It is common for serious illnesses or deaths of family members or friends to trigger hypochondria in certain individuals. Similarly, when approaching the age of a parent's premature death from disease, many otherwise healthy, happy individuals fall prey to hypochondria. These individuals believe they are suffering from the same disease that caused their parent's death, sometimes causing panic attacks with corresponding symptoms.

A majority of people who experience physical pains or anxieties over non-existent ailments are not actually "faking it", but rather, experience the natural results of other emotional issues, such as very high amounts of stress.