OBJECTIVES: We aimed to systematically review and assess published estimates of the cost of developing new drugs. METHODS: We sought English language research articles containing original estimates of the cost of drug development that were published from 1980 to 2009, inclusive. We searched seven databases and used citation tracing and expert referral to identify studies. We abstracted qualifying studies for information about methods, data sources, study samples, and key results. RESULTS: Thirteen articles were found to meet our inclusion criteria. Estimates of the cost of drug development ranged more than 9-fold, from USD$92 million cash (USD$161 million capitalized) to USD$883.6 million cash (USD$1.8 billion capitalized). Differences in methods, data sources, and time periods explain some of the variation in estimates. Lack of transparency limits many studies. Confidential information provided by unnamed companies about unspecified products forms all or part of the data underlying 10 of the 13 studies. CONCLUSIONS: Despite three decades of research in this area, no published estimate of the cost of developing a drug can be considered a gold standard. Studies on this topic should be subjected to reasonable audit and disclosure of - at the very least - the drugs which authors purport to provide development cost estimates for.