The need for induced hypotension in orthognathic surgery was evaluated. Blood loss, duration of operation, quality of the surgical field, and surgical result were measured in 36 patients, assigned to either hypotension (mean arterial pressure, MAP, 50-64 mmHg) or normotension (MAP > or = 65 mmHg). Hypotension was achieved by increasing the amount of isoflurane given. The hypotensive group had significantly less bleeding over time (mean 0.9 ml/minute, 95% confidence interval (CI) of mean 0.6 to 1.2, compared with 1.8, 95% CI 1.3 to 2.4, p = 0.005). The corresponding difference in total blood loss did not differ significantly between the groups (mean 186 ml, 95% CI 98 to 275, compared with 304, 95% CI 210 to 399). No patient required transfusion of red cells. Neither the duration of surgery, nor the quality of the surgical field, nor the final result were significantly influenced by hypotension. The clinical relevance of induced hypotension in orthognathic surgery must be considered to be doubtful. A mean reduction of less than 150 ml will be of limited value at the low levels of blood loss reported.