In a prospective cohort study 122 patients with herniated intervertebral lumbar disc and no previous low back surgery preoperatively were assessed regarding medical history, anthropometric and biological background variables. The outcome of surgery (traditional methods) was evaluated one year postoperatively, mainly using a composite Clinical Overall Score (COS), including pain intensity, physical signs, functional capacity and analgesics. Return to work was also assessed. In regression analyses, low body height, high values of weight and body mass index, as well as long duration of sickness absence were shown to be significantly related to a poor outcome, as evaluated by the COS. However, after controlling for modifying effects of previously determined predictive fibrinolytic and psychological variables, the background variables lost their significance. Female sex, low stature, long duration of sickness absence and physically strenuous work activities were statistically significantly related to lower frequencies of return to work.