The influence of low-back trouble on lumbar sagittal mobility was explored In 958 Individuals aged 10 to 84 years. Experience of low-back trouble was determined by questionnaire, and categorized as none, a previous history, or a current spell. Maximal mobility was estimated from flexlcurve records of back surface curvature. The results for adults revealed that mean mobility values were reduced by both previous and current low-back trouble, particularly in the upper lumbar region, when compared with nonsufferers. Stepwise regression analyses showed that variation in mobility was best accounted for by the cumulative effects of age and sex. These variables accounted for approximately one-third of the variation In mobility: low-back trouble only accounted for an additional 1%. At the extremes of the range, both hypomoblllty and hypermobility were Identified as risk Indicators for low-back trouble. Relative hypermobllity was not confined to subjects with no history of back trouble; some current sufferers had particularly high levels of mobility. Similarly hypomobillty was found In nonsufferers as well as in those with back trouble. The data Indicated that young adults (notably males) with previous low-back trouble may not recover their previous mobility on symptomatic resolution. The finding of hypermobility In current sufferers indicates that mobilization therapy may not be appropriate for such patients.