The aim of the investigation was to survey the period prevalence of musculoskeletal complaints among Swedish professional drivers. 460 out of 570 male drivers answered a postal inquiry. The period prevalence of musculoskeletal complaints was highest for the low back, the shoulders, the knees and the neck, in that order. For some parts of the musculoskeletal system the period prevalence of complaints tended to increase with age. A subdivision of the examined group of drivers according to task revealed--after standardizing for age (SRR)--different relative risk of complaints in various anatomical regions of the body. The interaction among some variables was studied by means of Automatic Interaction Detection Analysis. The analysis showed that the variables age and task reduced the variance of the period prevalence of musculoskeletal complaints most.