The failure to diagnose a condition is a severe misdiagnosis if a doctor fails to identify the condition. The majority of malpractice lawsuits are caused by the failure to diagnose conditions such as heart attack (http://www.wrongdiagnosis.com/h/heart_attack/intro.htm), breast cancer (http://www.wrongdiagnosis.com/b/breast_cancer/intro.htm), appendicitis (http://www.wrongdiagnosis.com/a/acute_appendicitis/intro.htm), lung cancer (http://www.wrongdiagnosis.com/l/lung_cancer/intro.htm), and colon cancer (http://www.wrongdiagnosis.com/c/colorectal/intro.htm). However, these are not actually the most prevalent undiagnosed conditions; see How Common is Failure to Diagnose? (http://www.wrongdiagnosis.com/intro/notdiagcommon.htm) for a list of conditions with their undiagnosed prevalence estimates.
Note that failure to diagnose a condition can also arise in conditions where a person has no symptoms (http://www.wrongdiagnosis.com/sym/no_symptoms.htm) or only mild symptoms (http://www.wrongdiagnosis.com/symptom/mild-symptoms.htm) and so never seeks medical advice (http://www.wrongdiagnosis.com/intro/never.htm). In fact this is often the case with the early stages of the above-mentioned cancers.
However, once you seek medical advice for symptoms, a failure-to-diagnose misdiagnosis is possible. This can occur if the doctor finds nothing wrong, or if the doctor makes the wrong diagnosis (http://www.wrongdiagnosis.com/intro/wrongdiag.htm) of another condition. There are numerous conditions that tend to be under-diagnosed (http://www.wrongdiagnosis.com/intro/underdiag.htm).