Résumé : This was a double-blind, parallel-group, multiple-dose study designed to compare the efficacy and tolerability of the sustained-release (SR) formulations of ibuprofen and diclofenac sodium for patients suffering from chronic back pain. The patients were randomly allocated to treatment with either the recommended once-daily dosage of ibuprofen SR (1600 mg) or diclofenac SR (100 mg) for 14 days; 30 patients were treated with ibuprofen and 32 with diclofenac. Clinical assessments of the patients' back condition were made at the beginning and end of the study, and the patients themselves rated their quality of sleep, level of activity, and severity of pain each day. In terms of efficacy, the ibuprofen SR treatment resulted in a trend toward better patient responses for all variables other than quality of sleep and night pain, although differences between the two treatment groups were not statistically significant. There were eight patient withdrawals in the diclofenac SR group (six due to adverse events) compared with four patients in the ibuprofen SR group (only one attributed to adverse events). Overall, 16 diclofenac SR-treated patients reported 24 adverse events, 8 of which were recorded as definitely related to the drug. Four ibuprofen SR-treated patients reported a total of nine adverse events, and only three were considered to be definitely drug related. The difference between the groups in the number of patients reporting adverse events was statistically significant (P = 0.002). The demonstrated efficacy and superior tolerability of ibuprofen SR provide strong support for the use of this once-daily formulation in the management of patients with chronic back pain.