The narrow ICD-10 and DSM-IV definition of hypochondriasis makes it a rarely used diagnosis. Based on a latent class analysis of the symptoms exhibited by 701 patients (ages 18-65) in general practice, a new and more valid hypochondriasis diagnosis was defined in this study. The main symptom is "obsessive rumination about illnesses", and the patient must also have at least one of five other symptoms. The prevalence was 9.5 for both genders. There was a good agreement between the diagnoses made during the psychiatric interview and the physicians' assessments.