Periradicular therapy (PRT) has become popular in the treatment of lumbar radicular complaints, both primary, due to disc herniations (Group 1), and postoperative, following disc surgery (Group 2). However, hitherto reported data on 'periradicular injections' are more of a technical nature. The present study was designed to evaluate the therapeutic success of CT- versus fluoroscope-guided periradicular injections of local anaesthetics and corticoids, and to investigate the impact of imaging procedures on the results. We report on 80 patients who underwent CT-guided (n = 40) or fluoroscope-guided (n = 40) PRT for lumbar radicular irritation since April 1993. Forty patients had primary nerve root irritation due to disc protrusion, and 40 suffered from postoperative epidural fibrosis. Follow-up consisted in a clinical examination and an interview one day after each injection as well as 1 and 6 months later. Assessment was based on a score taking into account the clinical findings, the patient's complaints, and the patient's evaluation. Six months following treatment there was a significant reduction of ischialgia in both Groups 1 and 2 (p < 0.001). However, the results were significantly poorer in Group 2 (postoperative). Among the patients not operated on, those who underwent CT-guided injections had a significantly better outcome (p < 0.001). PRT had no significant influence on low back pain or pseudoradicular syndromes. The improvement of sensory disturbances achieved by both CT- and fluoroscope-guided injections in patients not previously submitted to surgery is statistically significant (p < 0.05). As compared to Group 1 (no surgery), the positive effects in patients of Group 2 were of significantly shorter duration (p < 0.05). Motor deficits were not influenced by the treatment. Long-term follow-up shows that there is no positive effect in those patients in whom the first two PRT attempts had failed. Thus, PRT represents a useful long-term therapeutic alternative for lumbar radicular syndromes, particularly when due to primary discogenic compression. CT-guided injection is superior to fluoroscope-assisted treatment for both its visualization and its longer-lasting effect.