Data from the 1978 Social Security Survey of Disability and Work indicate that most chronic diseases in the age 18-64 population are reported significantly more frequently by individuals with fewer than 12 years of formal education. Of the 23 health conditions reported by more than 1% of the population, 19 differed significantly in reported frequencies according to formal educational level. The relative frequencies of any reported condition in individuals with 1-8, 9-11, 12 years, and more than 12 years of formal education, were 3.6, 2.3, 1.4 and 1.0 respectively. Significant trends according to formal educational level were seen for all types of chronic diseases, including cardiovascular, gastrointestinal, musculoskeletal, neoplastic, psychiatric, pulmonary and renal diseases. These trends remained significant for all categories except neoplastic disease when formal education was controlled for age, sex, race and smoking, suggesting that formal educational level may identify a marker in the pathobiology of disease of importance comparable to these other demographic variables.