In this study the relationship between low back pain and the following factors was studied: Clinical findings, frequency and duration of absenteeism, social situation, psychosomatic and psychological factors and the working environment. The sample studied included 220 persons (participation frequency 86%) between the ages of 16-65 who had either acutely declared themselves unable to work because of low back pain (acute patients, n = 50) or who had been ill because of low back pain for one month (subacute patients, n = 50) or for three months (chronic patients, n = 70). A control group (n = 50) consisting of persons who had not been absent at all from work the last year was also included. Information regarding the participants' socio-economic situation, previous and present illnesses, further sick-listing during the one year follow-up period and the duration of absenteeism was obtained from the records of the Department of Health Insurance. The median age for men (68%) in the four different groups was 46, 46, 46 and 48.5, respectively. The corresponding figures for women were 50, 33, 33 and 49 years. Twenty percent were of foreign extraction. The proportion of foreigners in the group of non-participants (n=33) was higher (39%) and in this group there was a significantly greater frequency of previous episodes of ill health of short duration (less than or equal to 7 days + no certificate of ill health). Despite a careful clinical examination it was not possible to find any objective signs amongst 51% (86) of the patients. These patients exhibited normal motion of the back, normal musculature, no signs of neurologic involvement, negative straight-leg-raising test, no fixed painful position and no pain during percussion or palpation despite the fact they had subjective symptoms. The proportion of patients without objective findings increased with increased duration of absenteeism. Forty percent of the acute back patients displayed no objective findings. The corresponding figures for the subacute and chronic back patient groups were 34% and 70%, respectively. In the group without objective findings but with chronic pain (greater than 3 months) there was an increased frequency of Waddell's non-organic signs compared with the group with objective findings. Psychological and social problems increased with increasing duration of absenteeism. There were significantly more patients with psychiatric illness, signs of alcoholism and early retirement in the three months group compared to the remaining groups.(ABSTRACT TRUNCATED AT 400 WORDS)