OBJECTIVE: To investigate the association between chronic exposure to second hand smoke (SHS) and the short-term prognosis of patients hospitalised with acute coronary syndromes. METHODS: Between 1 October 2003 and 30 September 2004, 2172 consecutive patients enrolled with acute coronary syndromes at the cardiology clinics or the emergency units of six major hospitals, in Greece were studied. Exposure to SHS was measured through a questionnaire administered during a specific interview, after the second day of hospitalisation. The main outcome of interest was the 30-day status of these patients (death, or rehospitalisation due to coronary heart disease). RESULTS: 1003 (46%) of the patients were exposed to SHS. Patients reporting exposure to SHS had 61% (95% CI 14% to 118%) higher risk of having an event during the first 30 days after hospitalisation as compared with patients who were not exposed to SHS, after taking into account the effect of several potential confounders. A dose-response linear relationship was observed between the risk of having recurrent events and the years of exposure to SHS (rho = 0.17, p<0.001). CONCLUSIONS: Exposure to SHS increases considerably the risk of recurrent events in patients who had survived a cardiac event.