57 patients who underwent surgery for slipped lumbar disc for the first time were examined prospectively 6 months after surgery for the purpose of deciding the correlation between the outcome of surgery and social and psychological factors. The following factors were found to be of importance: Female sex, action for damages, prolonged disease of the back; prolonged, current attack, report of long-term illness, pathological pain producing, anxiety, depression and multiple somatic complaints revealed by Minnesota Multiple Personality Inventory (MMPI), severe pain reported immediately post-operatively, employment and the presence of complete herniation at surgery. A closer study revealed 3 factors which were important independently and which explained the other factors: Admission of symptom scale (Ad) in the MMPI, the duration of the current attack and whether the patient was employed. On this basis we define a group with severe psychological and social strain (PASS), 57% of which had a poor outcome. 5% of the rest of the patients had a poor outcome. With the pre-operative assessment of whether or not the patients are under severe psychological and social strain, the outcome of surgery could be predicted correctly in 86% of the patients.