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When new drugs come to market and are pre-scribed by physicians to real-world patients,their costs and effectiveness may vary consider-ably from those measured in carefully controlled random-ized controlled trials (RTCs). Physicians, patients and provincial governments that fund pharmacare programs must base their prescribing and funding (coverage) deci-sions on the very limited information available from RCTs. In the real world, such drugs are prescribed not only for the relatively healthy and usually younger patients who enter RCTs, but also for patients with comorbidities and for older patients. As well, serious but less common side effects might not be detected in clinical trials; if any are detected, their frequency may not be precisely deter-mined. Thus the real-world cost-effectiveness may not mirror that shown in RCTS. In this issue, Laupacis and colleagues (see page 1167),