39 Background Therapy for acute stroke using rtPA was approved in Canada in February 1999. The Canadian Activase for Stroke Effectiveness Study Group was formed to study the use of rtPA in Canada in a 30-month post-marketing study. Purpose To both prospectively assess the safety of rtPA in the Canadian context and to examine whether the efficacy of rtPA for acute stroke, demonstrated in the NINDS trial, can be translated into effectiveness in routine clinical practice across Canada. Methods The CASES group is a collaboration among the Canadian Stroke Consortium (CSC), the Canadian Stroke Society, the Heart & Stroke Foundation of Canada, Hoffman-LaRoche Canada and physicians across the country. Centres across the country were registered and recruitment is ongoing. The study protocol has been approved by the research ethics board at each centre. Demographics, stroke risk factors, blood pressure, biochemistry, hematology, and CT scans are being collected. NIHSS and mRS scores are being collected prospectively. Outcomes will be monitored at discharge and at 3 months. Results In the first 20 months,72 centres are registered and 525 patients have been treated. The median NIHSS score is 14 (range 2–35). 30% of patients have minimal or no neurological deficit (NIHSS 0–1)and 47% are independent (mRS 0–2) at 90 days. The symptomatic hemorrhage rate is 4.0% (95%CI 2.5% to 6.0%). Multivariate analysis has failed to identify predictors of symptomatic ICH. The rate of protocol violations is 10%, the majority of which are time window violations. Based upon a phone survey of hospitals in Canada with CT scanners, the data set is 75% complete. Conclusions CASES is an ongoing prospective evaluation of the effectiveness of rtPA in acute stroke. The symptomatic hemorrhage rate is low (4.0%). Alteplase for ischemic stroke is safe and effective in Canada.