This study was designed to evaluate how new treatment guidelines of acute coronary syndrome (ACS) without ST elevation have been implemented in clinical practice especially in diabetic patients. A prospective follow-up was performed on 501 consecutive patients with suspected ACS without ST elevation admitted to nine hospitals in Finland between 15 January and 11 March 2001. The study group included 143 (29%) diabetic patients. Their risk profile was more severe than in non-diabetic patients; ST-depression on admission electrocardiography 57 versus 38%; P<0.0001, elevated troponin levels 66 versus 56%; P<0.05. Six months composite incidence of death, new myocardial infarction (MI), refractory angina or readmission for unstable angina was 39% in diabetic patients and 20% in non-diabetic patients (P<0.0001). In spite of this more severe risk profile, glycoprotein (GP) IIb/IIIa receptor antagonists and statins were used with similar frequency in non-diabetic and diabetic patients (15 vs. 19 and 48 vs. 54%, respectively; P=NS for both). In diabetic patients mean delay for in hospital coronary angiography was longer (6.4 vs. 4.2 days, P<0.05) and it was performed less often (32 vs. 45% P<0.05). Our results show that diabetic patients with ACS have higher risk profile and worse outcome than non-diabetic patients. Despite their indisputable benefits in diabetic patients, statins, GP IIb/IIIa receptor antagonists and invasive strategy were underused or often neglected. Further education is needed to change attitudes and to better implement new guidelines into clinical practice.