In an epidemiological study of acute herniated lumbar intervertebral discs in the New Haven, Connecticut (U.S.A.), area, it was found that this condition was most likely to be diagnosed among persons in the age group 30-39 years, and that the most important risk factors among the variable considered in this study were driving of motor vehicles at or away from work, sedentary occupations, suburban residence, and previous full-term pregnancies. Variables for which there was some suggestion of an association but for which the evidence was inconclusive were the male sex, high social class among females, chronic cough and chronic bronchitis, participation in baseball, golf and bowling, the spring and fall seasons, and possibly lack of physical activity other than at work. No increase in risk for this condition was related to race, social class in males, smoking habits, participation in sports other than baseball, golf and bowling, weight or body bulk, recent episodes of emotional stress, pregnancies which were not full-term, and jobs involving lifting, pushing, pulling, or carrying.