BACKGROUND: There is a lack of evidence regarding the value of tools designed to aid decision making in patients with newly diagnosed hypertension. AIM: To evaluate two interventions for assisting newly diagnosed hypertensive patients in the decision whether to start drug therapy for reducing blood pressure. DESIGN OF STUDY: Factorial randomised controlled trial. SETTING: Twenty-one general practices in south-west England, UK. METHOD: Adults aged 32 to 80 years with newly diagnosed hypertension were randomised to receive either: (a) computerised utility assessment interview with individualized risk assessment and decision analysis; or (b) information video and leaflet about high blood pressure; or (c) both interventions; or (d) neither intervention. Outcome measures were decisional conflict, knowledge, state anxiety, intentions regarding starting treatment, and actual treatment decision. RESULTS: Of 217 patients randomised, 212 (98%) were analysed at the primary follow-up (mean age = 59 years, 49% female). Decision analysis patients had lower decisional conflict than those who did not receive this intervention (27.6 versus 38.9, 95% confidence interval [CI] for adjusted difference = -13.0 to -5.8, P < 0.001), greater knowledge about hypertension (73% versus 67%, adjusted 95% CI = 2% to 9%, P = 0.003) and no evidence of increased state anxiety (34.8 versus 36.8, adjusted 95% CI = -5.6 to 0.1, P = 0.055). Video/leaflet patients had lower decisional conflict than corresponding controls (30.3 versus 36.8, adjusted 95% CI = -7.4 to -0.6, P = 0.021), greater knowledge (75% versus 65%, adjusted 95% CI = 6% to 13%, P < 0.001) and no evidence of increased state anxiety (35.7 versus 36.1, adjusted 95% CI = -3.9 to 1.7, P = 0.46). There were no differences between either of the interventions and their respective controls in the proportion of patients prescribed antihypertensive medication (67%). CONCLUSIONS: This trial demonstrates that, among patients facing a real treatment decision, interventions to inform patients about hypertension and to clarify patients' values concerning outcomes of treatment are effective in reducing decisional conflict and increasing patient knowledge, while not resulting in any increases in state anxiety.