OBJECTIVE: To determine whether, in acute non-ST elevation coronary syndrome, the benefit from early invasive coronary intervention compared with a conservative strategy of later symptom-guided intervention varies over time. METHODS: In RITA 3 (Randomised Intervention Trial of unstable Angina 3) patients were randomly assigned to coronary angiography (median 2 days after randomisation) and appropriate intervention (n = 895) or to a symptom-guided conservative strategy (n = 915). RESULTS: In the first week patients in both groups were at highest risk of death, myocardial infarction (MI) or refractory angina (incidence rate 40 times higher than in months 5-12 of follow up). There were 22 MIs and 6 deaths in the intervention group (largely due to procedure-related events, 14 MIs and 3 deaths) versus 17 MIs and 3 deaths in the conservative group. In the rest of the year there were an additional 12 versus 27 MIs, respectively (treatment-time interaction p = 0.021). Over one year in the intervention group there was a 43% reduction in refractory angina; 22% of patients underwent coronary artery bypass surgery and 35% underwent percutaneous coronary intervention only, which reduced refractory angina but provoked some early MIs; and 43% were still treated medically, mostly because of a favourable initial angiogram. CONCLUSION: Any intervention policy needs to recognise the high risk of events in the first week and the substantial minority of patients not needing intervention. Intervention may be best targeted at higher risk patients, as the early hazards of the procedure are then offset by reduced subsequent events.