Design Randomised controlled trial Intervention Patients aged ≥16 years requiring non-surgical extraction were randomised into three groups. Group A (n = 40) were instructed to gargle six times daily with warm saline and group B (n = 40) twice daily; group C (n = 40) were not instructed to gargle with warm saline and served as controls. All patients received the same oral antibiotics and analgesics, and similar postoperative instructions, except regarding saline rinses. Mouth rinsing was to start 24 hours after the procedure and patients were reviewed at 72 hours. Outcome measure The patients were evaluated 72 h post-operatively for the presence of alveolar osteitis, acute inflamed socket and acute infected socket by an independent observer who was blinded to the treatment group. Results One hundred and twenty patients were randomised (40 per group). The overall prevalence of alveolar osteitis was 10.0% and that of acute inflamed socket was 25.0%. No cases of acute infected socket were observed. There was a statistically significant difference between the study groups with respect to the development of alveolar osteitis (x2 = 15.43, df = 2, P = 0.001), but not for acute inflamed socket, with only 2.5% of the saline groups (2 out of 80) developing alveolar osteitis compared with 25% (10 of 40) in the control group. Conclusions The instruction to use warm saline mouth rinse is beneficial in the prevention of alveolar osteitis after dental extractions. There is no significant difference in the efficacy of the twice-daily warm saline mouth rinse regimen compared to the six times daily regimen. The twice-daily saline mouth rinse regimen is more convenient, and patient compliance may be better than with the six times daily rinse routine.