The intensity of work recovery in LBP has been studied using the National Health Register. Nine hundred forty men, 40-47 years old, were selected randomly from the census register of the city of Göteborg, Sweden. Sickness absence data were obtained from the Health Register, in which all sickness absence from age 16 is recorded. The rate of return to work decreases as expected with an increase in absence period. Different rates were found for different diagnoses, however, with low return intensities in patients with sciatica compared with those with back pain, ie, return to work was slower in patients with sciatica. Men with manual work had a significantly longer average sickness absence than white-collar workers. The intensity of work recovery was lower in blue-collar workers during the first 20 days of absence, while the reverse was true after 20 days of sickness absence, ie, the white-collar workers who were absent more than 20 days had a slower rate of recovery than blue-collar workers who had been absent for 20 days. Data as presented here can be used to study the effect of intervention (for example, manual therapy) on the natural course of work recovery. It also can be used, as above, to study differences in sickness absence patterns between different diagnoses and work groups.