Hospital admissions for herniated lumbar intervertebral disc or sciatica were followed up over a period of 11 years in 57,000 men and women who had participated in medical check-ups in various parts of Finland. Information on their hospitalizations after the baseline examination was obtained by record linkage to the National Hospital Discharge Register. To identify factors predicting back diseases, four controls matched individually for sex, age and place of residence were chosen for each of the 592 incidence cases who were free from severe back trouble and aged 20-59 at entry. Low or intermediate social class and blue-collar occupations in services or industry in men and symptoms suggesting psychological distress in women proved significant predictors for hospitalization due to herniated lumbar disc or sciatica. An association with the risk was suggested for smoking or chronic cough in men and parity in women. Marital status or leisure time physical activity were not predictive of herniated lumbar intervertebral disc or sciatica.