In a population of 240 male fork-lift truck drivers who drove at least 4 h daily, the occurrence of low-back trouble was studied in relation to that of two reference groups. The participation rate of the fork-lift truck drivers was 88%. The responses to a questionnaire concerning low-back trouble were reviewed. Among the fork-lift truck drivers, a statistically significant higher occurrence of low-back trouble was reported for the year preceding the study, in comparison, according to age, to that of a reference group of 399 working men (65 against 47%); however, there was no significantly increased frequency when compared to that of a reference group of 66 unskilled male workers (65 against 51%). The fork-lift truck drivers had a significantly higher rate of absence from work within the previous year due to low-back trouble than the two reference groups (22% compared to 7 and 9%). These findings were confirmed during the follow-up year. A correlation was found between length of employment as a fork-lift truck driver and the occurrence of low-back trouble within the preceding year. It was concluded that fork-lift truck driving may be a contributory cause for low-back trouble.