Injuries to the low back are the most common cause for injury claims among material handlers. Previous studies have shown conflicting results about how age affects risk of low-back injury. This study describes the incidence of acute low-back injury by age, gender, length of employment, and lifting intensity measured by job classification in a cohort of material handlers. The cohort included all material handlers employed at a large home improvement retail chain in California from 1989 through 1994. The cohort accrued approximately 50,000 full time equivalents over the study period. A total of 2152 low-back injuries were reported during the study period. Compared to workers aged younger than 45, the crude rate ratio for workers aged 45 to 54 was 0.78, and for workers aged 55 and above was 0.84. However, this age difference was not apparent among length of employment strata or among jobs with low or medium lifting intensity. A higher proportion of workers over the age of 55 missed work time because of their injury, and workers over 45 had a higher average number of lost workdays per injury. This research indicates that workers over age 55 had similar injury rates to workers younger than age 55, even when considering lifting intensity and length of employment. However, their injuries may cause a longer period of disability.