Lifestyle factors such as smoking, obesity, and level of physical activity predict low back pain (LBP) and sciatica. The authors investigated whether participating in sports, smoking, and being overweight or obese at 14 years of age predicted hospitalizations due to LBP or sciatica in adulthood. In 1980, at the age of 14 years, a total of 11,399 members of the 1966 Northern Finland Birth Cohort returned the postal questionnaire. Patients from the 1966 Northern Finland Birth Cohort who were hospitalized because of LBP or sciatica were followed to the end of 2008 through the Finnish Hospital Discharge Register. Data were analyzed using Cox’s proportional hazards multistate model with the Markov clock forward time scale. During follow-up, 119 females (2.7%) and 254 males (5.6%) had been hospitalized at least once because of LBP or sciatica. Among females, overweight was associated with an increased risk of second-time hospitalization for surgical treatment for sciatica (hazard ratio = 7.1, 95% confidence interval: 1.5, 34.4). Among males, smoking was associated with an increased risk of first-time nonsurgical hospitalization (hazard ratio = 1.8, 95% confidence interval: 1.2, 2.7) and second-time surgical hospitalization (hazard ratio = 3.2, 95% confidence interval: 1.2, 8.2). The authors found potentially modifiable risk factors in adolescence that predicted hospital treatments for low back disorders during adolescence and young adulthood.