ABSTRACT— From a large series of delusional subjects 23 patients demonstrated hypochondriacal delusions as the main delusion during the long-term course of approximately 30 years. An extensive study of these cases reveals that the majority had abnormal premorbid personality, especially somatization, paranoid and/or avoidant traits. Previous and/or precipitating somatic illnesses, if present, were not very serious. The hypochondriacal preoccupation diminished in the long term, but the overall prognosis varied, as the patients did not belong to a uniform diagnostic category. Implications for the clinician in diagnosing and treating are discussed, and the importance of early detection of correct diagnostic category is stressed.