Of all 30-, 40-, 50-, and 60-year-old inhabitants of Glostrup, a suburb of Copenhagen, 82% (449 men and 479 women) participated in a general health survey, which included a thorough physical examination relating to the lower back. The examination was constituted of anthropometric measurements, flexibility/elasticity measurements of the back and hamstrings, as well as tests for trunk muscle strength and endurance. The reproducibility of the tests was found to be satisfactory. Twelve months after the physical examination 99% of the participants completed a questionnaire sent by mail concerning low back trouble (LBT) in the intervening period. The prognostic value of the physical measurements was evaluated for first-time experience and for recurrence or persistence of LBT by analyses of the separate measurements and discriminant analyses. The main findings were that good isometric endurance of the back muscles may prevent first-time occurrence of LBT in men and that men with hypermobile backs are more liable to contract LBT. Recurrence or persistence of LBT was correlated primarily to the interval since last LBT-episode: the more LBT, the shorter the intervals had been. Weak trunk muscles and reduced flexibility/elasticity of the back and hamstrings were found as residual signs, in particular, among those with recurrence or persistence of LBT in the follow-up year.